Add bounding rects to the captionBar() inset source

In desktop mode, the caption used for freeform windows has a big space
of empty space between the app chip and the window control buttons.
To allow apps to utilize that empty space, this CL reports the chip
and control btns as bounding rects to the inset system, so that apps
can avoid overlapping with them when drawing e2e behind the caption bar.

Bug: 316387515
Test: m
Change-Id: Id7261e4a3996628079068db23b5d68cbafe79c0e