Given we have updated API extractor to the most recent
version, we need to update the API goldens because the
latest version uses alias exports to avoid collisions with
default library globals (like `Event`).
PR Close#42737
Moves the public api .d.ts files from tools/public_api_guard to
goldens/public-api.
Additionally, provides a README in the goldens directory and a script
assist in testing the current state of the repo against the goldens as
well as a command for accepting all changes to the goldens in a single
command.
PR Close#35768