[InputVizard] Make OverscrollControllerAndroid an input event observer.

This CL modifies OverscrollControllerAndroid to directly observe input
events by doing the following:
1. Makes OverscrollControllerAndroid a
   RenderWidgetHost::InputEventObserver. This allows
   OverscrollController to keep getting notified of discrete input
   events such as GSB/GestureFlingStarts. Since GSUs are not notified
   using InputEventObservers, OverscrollController will now directly
   consume MotionEvents instead, see point 2.
2. Once an overscroll is identified, OverscrollControllerAndroid will
   now directly consume MotionEvents instead of GestureEvents to update
   the refresh effect and cease further propagation of the input events
   (from RenderWidgetHostViewAndroid::OnTouchEvent).
3. OverscrollRefresh now uses 'accumulated_overscroll' information from
   DidOverscrollParams instead of capturing scroll deltas from GSUs.
   This change shouldn't impact the behavior since `cumulative_scroll_`
   was only being tracked to capture the direction of overscroll, which
   can be captured using `-accumulated_overscroll`.
4. This CL modifies the current behavior where the refresh effect is
   stopped when a pinch zoom is identified. This is inline with UX
   guidelines to commit to one gesture instead of mixing multiple
   gestures with InputVizard.
5. Fixes some tests because of the changes in
   OverscrollControllerAndroid.

Bug: b:365985685
Change-Id: I614c4840d6772d5f88f02e1628176a492d491b06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6352218
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Commit-Queue: Aman Verma <amanvr@google.com>
Cr-Commit-Position: refs/heads/main@{#1436783}