[context menu] adjust anchor if window is drawn edge-to-edge

AnchoredPopupWindow applies anchorRect assuming origin right below the
window decor.
The input touch point from ContextMenuParams are coordinates relative to
the associated RenderView's origin, i.e. the space not including the
window decor, tabstrip and toolbar. It also provides a vertical offset
of height of tabstrip + toolbar which will be added to the touch point
to compute the anchor rect.

This is correct when edge-to-edge is false, e.g. when window decor is
drawn independently from the tab strip (#tab-strip-layout-optimization
is disabled).
But edge-to-edge is true, i.e. window decor is tabstrip, the offset
will cause the anchor rect to be lower than the true touch point by the
height of tabstrip. See:
Before (flag off): https://screenshot.googleplex.com/8CMJqYcpPpwBdW8
Before (flag on): https://screenshot.googleplex.com/5om8UfsZG4mM3QJ

Therefore, when edge-to-edge is true, subtract from the offset the
height of tabstrip = height of window decor.
After (flag on): https://screenshot.googleplex.com/WCJ2GkgopWu44fQ
After (flag off): https://screenshot.googleplex.com/4WqccMYgnXgZj3Z

Bug: 400499940
Change-Id: Ic3c93901427aee2d246300b9ef76835d05d60a50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6629901
Commit-Queue: Grace Cham <hscham@chromium.org>
Reviewed-by: Sinan Sahin <sinansahin@google.com>
Auto-Submit: Grace Cham <hscham@chromium.org>
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1477101}