Fix ShortcutLoggingTests flaky tests.

Use TestLooper to finish all callbacks correctly to fix flakiness
caused due to handler callbacks being added on handler thread
itself which runWithScissors() call doesn't finish all together.

Test: atest ShortcutLoggingTests
Bug: 300023716
Change-Id: I29feec5188bdb3aa4b5297f5cf56969e36ca48a8
3 files changed