## Description

This adds a checker that will check all of the API docs examples to make sure that they are linked from at least one source file in the packages.

It also checks to make sure that all of the examples have an associated test. Since there are a large number that don't have tests at the moment, there is also a large exception list that can be burned down (burn down list is in https://github.com/flutter/flutter/issues/130459).

Because there are missing links currently, this PR will only pass after https://github.com/flutter/flutter/pull/130521 is merged.

## Related Issues

- https://github.com/flutter/flutter/issues/129956
- https://github.com/flutter/flutter/issues/130459

## Tests

- Added test for the checker.