```
export const __core_private_testing_placeholder__ = '';
```
This API should be removed. But doing so seems to break `google3` and
so it requires a bit of investigation. A work around is to mark it as
`@codeGenApi` for now and investigate later.
PR Close#38274
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