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.

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Co-authored-by: luoliwoshang <51194195+luoliwoshang@users.noreply.github.com>

_demo/go/issue1370_geometry/geometry/geometry.go

@@ -0,0 +1,26 @@
+package geometry
+
+type Shape interface {
+	Area() float64
+	validate() bool
+	setID(int)
+}
+
+type Rectangle struct {
+	Width, Height float64
+	id            int
+}
+
+func (r *Rectangle) Area() float64  { return r.Width * r.Height }
+func (r *Rectangle) validate() bool { return r.Width > 0 && r.Height > 0 }
+func (r *Rectangle) setID(id int)   { r.id = id }
+func (r *Rectangle) GetID() int     { return r.id }
+
+func NewRectangle(width, height float64) *Rectangle {
+	return &Rectangle{Width: width, Height: height}
+}
+
+func RegisterShape(s Shape, id int) error {
+	s.setID(id)
+	return nil
+}