Match first touch event's id to corresponding gestures

Match first touch event's id in a touch event sequence to all the
gestures generated from the original touch event sequence.
We'll name the first touch event id primary_unique_touch_event_id.

Use this primary touch event id to map gestures to corresponding
PointerEvent id for the pointer event sequence generated by the
original touch event sequence.

Bug: 1206108
Change-Id: I5ffd4248ad07e2e09b36908c4c2d077983708dc4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2889205
Commit-Queue: Liviu Tinta <liviutinta@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#909698}