Stop skipping 2 methods in config changes

To avoid duplicate configuration pushes Task introduced an override
onConfigurationChanged() method, which effectively bypassed 2 method
calls in WindowContainer#onConfigurationChanged(), and broke letterbox.

Stop bypassing those methods by overriding a different
onConfigurationChanges().

Bug: None
Test: Letterbox works.
Test: atest PinnedStackTests#testEnterPictureInPictureSavePosition
Change-Id: I66f000d5402e3a340e365e751be4df9eb765a452