[iOS] IPH Gesture Recognition Improvements

Adds 2 experiment params to the IPH ablation feature:
1. CancelTouchesInViewForIPH: Prevents touches from being queued when
dismissing an IPH. This is to validate a theory and is probably not
shippable. This prevents certain NTP actions from firing off, such as
tapping a feed article, since it will instead be used to dismiss the
IPH. However, most touches continue to be recognized since they last
for longer than 1 event (like a swipe).
2. IPHGestureRecognitionImprovement: Improves the handling of touch
events after the recognizers have been dismissed. The idea is that
touches are being queued and handled after the IPH has been dismissed,
leading to crashes.

Bug: 398211689
Change-Id: I4da8ad9867e1f590c2fb001e7f7c57b4365a8bf0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6394655
Auto-Submit: Adam Arcaro <adamta@google.com>
Commit-Queue: Adam Arcaro <adamta@google.com>
Reviewed-by: Ginny Huang <ginnyhuang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1438191}