refactor: move issue #1370 regression tests from _cmptest to _demo

Move the three regression test cases for issue #1370 from _cmptest/ to _demo/:
- 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/issue1370_geometry/geometry.go

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