refactor: move issue #1370 regression tests to _demo/go

Move the three regression test cases from _demo/ to _demo/go/:
- issue1370_gotypes (go/types.Object test)
- issue1370_goast (go/ast.Expr test)
- issue1370_geometry (custom interface test)

Updated import path in geometry.go to reflect new location.

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

_demo/go/issue1370_geometry/geometry.go

@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/goplus/llgo/_demo/issue1370_geometry/geometry"
+	"github.com/goplus/llgo/_demo/go/issue1370_geometry/geometry"
 )
 
 func main() {