Android: Replace onBackPressed with OnBackPressedDispatcher (2)

As a follow-up on crrev.com/c/3421446, replaces all the overridden
method |onBackPressed| in *Activity classes in Chrome with
OnBackPressedDispatcher/OnBackPressedCallback.

When a back press event is not handled, we disable the current callback
and call the dispatcher again to let other parties get a chance to
handle it. This was not necessary in 342146 for ChromeActivity which
is always at the bottom of the activity stack.

Bug: 1279941
Change-Id: I06cb9e20f171b741a9c7fd3218d9cf6cc68857b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3435248
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Reviewed-by: Jinsuk Kim <jinsukkim@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/main@{#968176}