Consume appropriate system bar insets when consuming caption bar insets

Caption bars are part of window insets - if one type of system bar insets are consumed, without also applying that change to the rest of the system bars, the InsetObserver may end up communicating misleading insets to future observers and consumers.

For example, suppose a caption bar of 100 pixels overlaps with a status bar of 50 pixels. Both bars are positioned from the top of the screen, so the caption bar extends 50 pixels below the bottom of the status bar. If an insets consumer consumes the caption bar inset of 100 pixels, but then leaves the status bar insets untouched, future consumers will believe they are in a window with only a 50 pixel status bar, and react accordingly, when in reality there should be no top inset, as the status bar is entirely within the bounds of the caption bar inset.

This change creates a subclass for InsetsRectProvider to account for caption bars, though it could be tweaked to be general to all system bars. When consuming insets, the consumed insets are also subtracted from the systemBars() insets, which automatically applies the change across the rest of the systemBars() insets (including status and navigation bars).

Bug: 394416443
Change-Id: Ie5a2a266c1242487bc79a3613774ec71e205642b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6331298
Commit-Queue: Charles Hager <clhager@google.com>
Reviewed-by: Aishwarya Rajesh <aishwaryarj@google.com>
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1432838}