Add LLVM IR test case for cross-package interface private method calls using go/types.Scope.Insert. This test verifies the fix in PR #1371 by checking the generated LLVM IR includes correct package path for interface metadata with private methods. Generated with [codeagent](https://github.com/qbox/codeagent) Co-authored-by: luoliwoshang <luoliwoshang@users.noreply.github.com>