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/_testrt/tpmethod/out.ll

@@ -37,7 +37,8 @@ source_filename = "github.com/goplus/llgo/cl/_testrt/tpmethod"
 @10 = private unnamed_addr constant [2 x i8] c"fn", align 1
 @11 = private unnamed_addr constant [4 x i8] c"Then", align 1
 @"*_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[error]]" = linkonce global ptr null, align 8
-@"_llgo_iface$kSla6xFkiJD3PX1RdCGebCgULXloNxgSHKPEQsXsqos" = linkonce global ptr null, align 8
+@"_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.Future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[error]]" = linkonce global ptr null, align 8
+@12 = private unnamed_addr constant [6 x i8] c"Future", align 1
 
 define %"github.com/goplus/llgo/runtime/internal/runtime.iface" @"github.com/goplus/llgo/cl/_testrt/tpmethod.ReadFile"(%"github.com/goplus/llgo/runtime/internal/runtime.String" %0) {
 _llgo_0:
@@ -129,14 +130,11 @@ _llgo_0:
   store { ptr, ptr } %0, ptr %2, align 8
   %3 = load ptr, ptr @"_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[error]]", align 8
   %4 = load ptr, ptr @"*_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[error]]", align 8
-  %5 = load ptr, ptr @"_llgo_func$wp7b63sFyNWPTd8VyEOOosByqpZg5pKsGThGMOTpyvo", align 8
-  %6 = load ptr, ptr @"github.com/goplus/llgo/cl/_testrt/tpmethod.struct$s_pTkk2q6m_bRjfPic11Z1ogmQ-VdSHpGxyzvfszwb8", align 8
-  %7 = load ptr, ptr @"_llgo_func$pIyBXw4qkUL3JRjAVf_wwtiGz7b0evOvoFHlctBJd6o", align 8
-  %8 = load ptr, ptr @"_llgo_iface$kSla6xFkiJD3PX1RdCGebCgULXloNxgSHKPEQsXsqos", align 8
-  %9 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.NewItab"(ptr %8, ptr %4)
-  %10 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.iface" undef, ptr %9, 0
-  %11 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.iface" %10, ptr %1, 1
-  ret %"github.com/goplus/llgo/runtime/internal/runtime.iface" %11
+  %5 = load ptr, ptr @"_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.Future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[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 linkonce void @"__llgo_stub.github.com/goplus/llgo/cl/_testrt/tpmethod.ReadFile$1"(ptr %0, { ptr, ptr } %1) {
@@ -525,24 +523,33 @@ _llgo_20:                                         ; preds = %_llgo_19, %_llgo_18
   %249 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.PointerTo"(ptr %248)
   call void @"github.com/goplus/llgo/runtime/internal/runtime.SetDirectIface"(ptr %249)
   store ptr %249, ptr @"*_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[error]]", align 8
-  %250 = load ptr, ptr @"_llgo_func$pIyBXw4qkUL3JRjAVf_wwtiGz7b0evOvoFHlctBJd6o", align 8
-  %251 = load ptr, ptr @"_llgo_iface$kSla6xFkiJD3PX1RdCGebCgULXloNxgSHKPEQsXsqos", align 8
+  %250 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.NewNamedInterface"(%"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @1, i64 42 }, %"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @12, i64 6 })
+  %251 = load ptr, ptr @"_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.Future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[error]]", align 8
   %252 = icmp eq ptr %251, null
   br i1 %252, label %_llgo_21, label %_llgo_22
 
 _llgo_21:                                         ; preds = %_llgo_20
-  %253 = insertvalue %"github.com/goplus/llgo/runtime/abi.Imethod" { %"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @11, i64 4 }, ptr undef }, ptr %250, 1
-  %254 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.AllocU"(i64 24)
-  %255 = getelementptr %"github.com/goplus/llgo/runtime/abi.Imethod", ptr %254, i64 0
-  store %"github.com/goplus/llgo/runtime/abi.Imethod" %253, ptr %255, align 8
-  %256 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" undef, ptr %254, 0
-  %257 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %256, i64 1, 1
-  %258 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %257, i64 1, 2
-  %259 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.Interface"(%"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @1, i64 42 }, %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %258)
-  store ptr %259, ptr @"_llgo_iface$kSla6xFkiJD3PX1RdCGebCgULXloNxgSHKPEQsXsqos", align 8
+  store ptr %250, ptr @"_llgo_github.com/goplus/llgo/cl/_testrt/tpmethod.Future[github.com/goplus/llgo/cl/_testrt/tpmethod.Tuple[error]]", align 8
   br label %_llgo_22
 
 _llgo_22:                                         ; preds = %_llgo_21, %_llgo_20
+  %253 = load ptr, ptr @"_llgo_func$wp7b63sFyNWPTd8VyEOOosByqpZg5pKsGThGMOTpyvo", align 8
+  %254 = load ptr, ptr @"github.com/goplus/llgo/cl/_testrt/tpmethod.struct$s_pTkk2q6m_bRjfPic11Z1ogmQ-VdSHpGxyzvfszwb8", align 8
+  %255 = load ptr, ptr @"_llgo_func$pIyBXw4qkUL3JRjAVf_wwtiGz7b0evOvoFHlctBJd6o", align 8
+  br i1 %252, label %_llgo_23, label %_llgo_24
+
+_llgo_23:                                         ; preds = %_llgo_22
+  %256 = insertvalue %"github.com/goplus/llgo/runtime/abi.Imethod" { %"github.com/goplus/llgo/runtime/internal/runtime.String" { ptr @11, i64 4 }, ptr undef }, ptr %255, 1
+  %257 = call ptr @"github.com/goplus/llgo/runtime/internal/runtime.AllocU"(i64 24)
+  %258 = getelementptr %"github.com/goplus/llgo/runtime/abi.Imethod", ptr %257, i64 0
+  store %"github.com/goplus/llgo/runtime/abi.Imethod" %256, ptr %258, align 8
+  %259 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" undef, ptr %257, 0
+  %260 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %259, i64 1, 1
+  %261 = insertvalue %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %260, i64 1, 2
+  call void @"github.com/goplus/llgo/runtime/internal/runtime.InitNamedInterface"(ptr %250, %"github.com/goplus/llgo/runtime/internal/runtime.Slice" %261)
+  br label %_llgo_24
+
+_llgo_24:                                         ; preds = %_llgo_23, %_llgo_22
   ret void
 }
 
@@ -568,8 +575,6 @@ declare void @"github.com/goplus/llgo/runtime/internal/runtime.InitNamed"(ptr, 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.NewItab"(ptr, ptr)
 
 attributes #0 = { nocallback nofree nounwind willreturn memory(argmem: write) }