Currently we extract all functions from the compilation unit - it doesn't really make sense as it will try to process functions in included files too.
As we require sapi_in flag, we have information which files are of interest.
This change stores the top path in _TranslationUnit and uses it when looking for function definitions to filter only functions from the path we provided.
PiperOrigin-RevId: 297342507
Change-Id: Ie411321d375168f413f9f153a606c1113f55e79a
