Reset toast rate limiting when it is manually enabled.

CTS tests can now use this to avoid hitting rate limits if there are
multiple tests which have rate limiting enabled (toast in one tests
won't count towards rate limiting in the other).

Test: atest android.widget.cts.ToastTest
Bug: 174841445
Change-Id: I0321e0aa6c8dab9c3ea99bbb5ca83b6fed822875