[TSLO] Update InsetsRectProvider#maybeUpdateWidestUnoccludedRect()'s
inset consumption conditions

Currently, insets are consumed whenever
maybeUpdateWidestUnoccludedRect() calculates a non-empty widest
unoccluded rect. This CL includes an update to allow an
InsetsRectProvider.Consumer to return a boolean when it has consumed
the rect update so that InsetsRectProvider can consume the insets only
when the consumer has reacted to the insets to adjust any views. This is
a more accurate reflection of when the insets should be consumed vs
always assuming that the insets will be consumed when the widest
unoccluded rect is non-empty.

The CL also removes the InsetsRectProvider.Observer interface in favor
of the Consumer interface since there is no immediate requirement to
purely observe rect changes other than observing for consumption.

This change also sets the foundation for a use case where a non-empty
widest unoccluded rect is not really indicative of the insets being
consumed, because of the nature of the unoccluded insets region, that
is addressed in the chained CL.

Bug: 418868898
Change-Id: I5ab6e93c9b7709f06154ef38a5899d0c7b604a81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6578386
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Commit-Queue: Aishwarya Rajesh <aishwaryarj@google.com>
Cr-Commit-Position: refs/heads/main@{#1467094}