Creates a separate bazel target for the google3 migration
tests. The benefit is that it's faster to run tests for
public migrations in development. Google3 lint rules are
usually another story/implementation and the tests are quite
slow due to how TSLint applies replacements.
Additionally if something changes in the google3 tslint rules,
the tests which aren't affected re-run unnecessarily.
PR Close#31817
Moves all google3 migration tslint rules into a single directory.
This makes it easier to wire up multiple migration rules in
google3 without having to update the rule directories each time
a new migration is available.
PR Close#30956
