fix(ssa): correct PkgPath for interface metadata in cross-package conversions

Fixes #1370 - Segmentation Fault When Calling Interface Private Methods Cross-Package

This commit fixes a critical bug where interface metadata's PkgPath was incorrectly
set when converting concrete type pointers to interfaces with private methods across
package boundaries.

Problem:
- When a concrete type pointer was converted to an interface with private methods
  in a package different from the interface definition package, the compiler
  incorrectly set the interface metadata's PkgPath to the current compilation
  package instead of the interface definition package
- This caused the runtime to only fill exported methods in the itab, leaving
  private method slots as NULL (0x0), resulting in segmentation faults

Solution:
- Modified abiInterfaceOf() in ssa/abitype.go to extract the package path from
  the interface's private methods (if any)
- Use that package path instead of the current compilation package path
- Fall back to current package path only if all methods are exported

Changes:
- ssa/abitype.go: Use abi.PathOf() to get correct package path
- ssa/interface.go: Refactor to simplify interface type handling
- Added comprehensive test cases and demos for go/types, go/token, and go/ast
- Updated all test outputs to reflect correct interface metadata generation

This fix resolves segmentation faults when using Go standard library interfaces
and user-defined interfaces with private methods across package boundaries.

Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: luoliwoshang <51194195+luoliwoshang@users.noreply.github.com>

cl/_testgo/errors/out.ll

@@ -19,8 +19,9 @@ source_filename = "github.com/goplus/llgo/cl/_testgo/errors"
 @3 = private unnamed_addr constant [5 x i8] c"Error", align 1
 @"_llgo_func$zNDVRsWTIpUPKouNUS805RGX--IV9qVK8B31IZbg5to" = linkonce global ptr null, align 8
 @"*_llgo_github.com/goplus/llgo/cl/_testgo/errors.errorString" = linkonce global ptr null, align 8
-@"_llgo_iface$Fh8eUJ-Gw4e6TYuajcFIOSCuqSPKAt5nS4ow7xeGXEU" = linkonce global ptr null, align 8
-@4 = private unnamed_addr constant [8 x i8] c"an error", align 1
+@_llgo_error = linkonce global ptr null, align 8
+@4 = private unnamed_addr constant [5 x i8] c"error", align 1
+@5 = private unnamed_addr constant [8 x i8] c"an error", align 1
 
 define %"github.com/goplus/llgo/runtime/internal/runtime.iface" @"github.com/goplus/llgo/cl/_testgo/errors.New"(%"github.com/goplus/llgo/runtime/internal/runtime.String" %0) {
 _llgo_0:
@@ -29,12 +30,11 @@ _llgo_0:
   store %"github.com/goplus/llgo/runtime/internal/runtime.String" %0, ptr %2, align 8
   %3 = load ptr, ptr @"_llgo_github.com/goplus/llgo/cl/_testgo/errors.errorString", align 8
   %4 = load ptr, ptr @"*_llgo_github.com/goplus/llgo/cl/_testgo/errors.errorString", align 8
-  %5 = load ptr, ptr @"_llgo_func$zNDVRsWTIpUPKouNUS805RGX--IV9qVK8B31IZbg5to", align 8
-  %6 = load ptr, ptr @"_llgo_iface$Fh8eUJ-Gw4e6TYuajcFIOSCuqSPKAt5nS4ow7xeGXEU", align 8
-  %7 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.NewItab"(ptr %6, ptr %4)
-  %8 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.iface" undef, ptr %7, 0
-  %9 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.iface" %8, ptr %1, 1
-  ret %"github.com/goplus/llgo/runtime/internal/runtime.iface" %9
+  %5 = load ptr, ptr @_llgo_error, align 8
+  %6 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.NewItab"(ptr %5, ptr %4)
+  %7 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.iface" undef, ptr %6, 0
+  %8 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.iface" %7, ptr %1, 1
+  ret %"github.com/goplus/llgo/runtime/internal/runtime.iface" %8
 }
 
 define %"github.com/goplus/llgo/runtime/internal/runtime.String" @"github.com/goplus/llgo/cl/_testgo/errors.(*errorString).Error"(ptr %0) {
@@ -60,7 +60,7 @@ _llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
 
 define void @"github.com/goplus/llgo/cl/_testgo/errors.main"() {
 _llgo_0:
-  %0 = call %"github.com/goplus/llgo/runtime/internal/runtime.iface" @"github.com/goplus/llgo/cl/_testgo/errors.New"(%"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @4, i64 8 })
+  %0 = call %"github.com/goplus/llgo/runtime/internal/runtime.iface" @"github.com/goplus/llgo/cl/_testgo/errors.New"(%"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @5, i64 8 })
   call void @"github.com/goplus/llgo/runtime/internal/runtime.PrintIface"(%"github.com/goplus/llgo/runtime/internal/runtime.iface" %0)
   call void @"github.com/goplus/llgo/runtime/internal/runtime.PrintByte"(i8 10)
   %1 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.IfacePtrData"(%"github.com/goplus/llgo/runtime/internal/runtime.iface" %0)
@@ -142,24 +142,31 @@ _llgo_4:                                          ; preds = %_llgo_3, %_llgo_2
   %37 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.PointerTo"(ptr %36)
   call void @"github.com/goplus/llgo/runtime/internal/runtime.SetDirectIface"(ptr %37)
   store ptr %37, ptr @"*_llgo_github.com/goplus/llgo/cl/_testgo/errors.errorString", align 8
-  %38 = load ptr, ptr @"_llgo_func$zNDVRsWTIpUPKouNUS805RGX--IV9qVK8B31IZbg5to", align 8
-  %39 = load ptr, ptr @"_llgo_iface$Fh8eUJ-Gw4e6TYuajcFIOSCuqSPKAt5nS4ow7xeGXEU", align 8
+  %38 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.NewNamedInterface"(%"github.com/goplus/llgo/runtime/internal/runtime.String" zeroinitializer, %"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @4, i64 5 })
+  %39 = load ptr, ptr @_llgo_error, align 8
   %40 = icmp eq ptr %39, null
   br i1 %40, label %_llgo_5, label %_llgo_6
 
 _llgo_5:                                          ; preds = %_llgo_4
-  %41 = insertvalue %"github.com/goplus/llgo/runtime/abi.Imethod" { %"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @3, i64 5 }, ptr undef }, ptr %38, 1
-  %42 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.AllocU"(i64 24)
-  %43 = getelementptr %"github.com/goplus/llgo/runtime/abi.Imethod", ptr %42, i64 0
-  store %"github.com/goplus/llgo/runtime/abi.Imethod" %41, ptr %43, align 8
-  %44 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" undef, ptr %42, 0
-  %45 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %44, i64 1, 1
-  %46 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %45, i64 1, 2
-  %47 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.Interface"(%"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @0, i64 40 }, %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %46)
-  store ptr %47, ptr @"_llgo_iface$Fh8eUJ-Gw4e6TYuajcFIOSCuqSPKAt5nS4ow7xeGXEU", align 8
+  store ptr %38, ptr @_llgo_error, align 8
   br label %_llgo_6
 
 _llgo_6:                                          ; preds = %_llgo_5, %_llgo_4
+  %41 = load ptr, ptr @"_llgo_func$zNDVRsWTIpUPKouNUS805RGX--IV9qVK8B31IZbg5to", align 8
+  br i1 %40, label %_llgo_7, label %_llgo_8
+
+_llgo_7:                                          ; preds = %_llgo_6
+  %42 = insertvalue %"github.com/goplus/llgo/runtime/abi.Imethod" { %"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @3, i64 5 }, ptr undef }, ptr %41, 1
+  %43 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.AllocU"(i64 24)
+  %44 = getelementptr %"github.com/goplus/llgo/runtime/abi.Imethod", ptr %43, i64 0
+  store %"github.com/goplus/llgo/runtime/abi.Imethod" %42, ptr %44, align 8
+  %45 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" undef, ptr %43, 0
+  %46 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %45, i64 1, 1
+  %47 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %46, i64 1, 2
+  call void @"github.com/goplus/llgo/runtime/internal/runtime.InitNamedInterface"(ptr %38, %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %47)
+  br label %_llgo_8
+
+_llgo_8:                                          ; preds = %_llgo_7, %_llgo_6
   ret void
 }
 
@@ -181,7 +188,9 @@ declare void @"github.com/goplus/llgo/runtime/internal/runtime.SetDirectIface"(p
 
 declare ptr @"github.com/goplus/llgo/runtime/internal/runtime.PointerTo"(ptr)
 
-declare ptr @"github.com/goplus/llgo/runtime/internal/runtime.Interface"(%"github.com/goplus/llgo/runtime/internal/runtime.String", %"github.com/goplus/llgo/runtime/internal/runtime.Slice")
+declare ptr @"github.com/goplus/llgo/runtime/internal/runtime.NewNamedInterface"(%"github.com/goplus/llgo/runtime/internal/runtime.String", %"github.com/goplus/llgo/runtime/internal/runtime.String")
+
+declare void @"github.com/goplus/llgo/runtime/internal/runtime.InitNamedInterface"(ptr, %"github.com/goplus/llgo/runtime/internal/runtime.Slice")
 
 declare ptr @"github.com/goplus/llgo/runtime/internal/runtime.NewItab"(ptr, ptr)