policy: minor perf opts and cleanup

Cleanup: Use more Maps instead of object dictionaries, use private fields instead of WeakMaps, minor error message cleanup.

Perf: Makes redirects lazier for parsing which was proving to be a large amount of work for relative URL strings and adds a parse cache.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines