[components] For https://github.com/mozilla-mobile/android-components/issues/11527 - Allow the decor view time to process the incoming insets
There was a race between how insets are applied when entering immersive mode
and enabling immersive mode restore by setting an insets listener which is now
resolved by ensuring the decor view has the time needed to process the incoming
insets, solution recommended on issuetracker
https://issuetracker.google.com/u/2/issues/
214012501 .
Removed the onWindowFocusChangeListener extension property since by having to
offer it through a getter the current implementation would always leak the old
one.
Fenix wasn't using it when this APIs allowed Fenix to pass such a listener and
there was no issue observed so there should be no observable negative impact.