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>