Fix #testChangeFontScaleNoRelaunch flaky

The test failed because we used public config diff to determine if
 Activity#onConfigurationChanged should be dispatched.
However, the public config diff contained the change which wouldn't
make Activity relaunch and also receive the callback.

This CL uses the public diff, which filters the change without
relaunching Activity, to determine if the callback should be
dispatched. This CL also covers the case that the callback is
still dispatched if small changes are handled.

Test: atest ActivityThreadClientTest ConfigChangeTests
Bug: 222067515
Bug: 222223467
Change-Id: I8aa80e9fd70fddc9f88a36e7dc2ffb2163b9ffa6