[PCCT] Expand/collapse the tab on soft keyboard state change

Expand the tab upon soft keyboard opens, and collapse it back when
closed. This makes it feasible for users to interact with the
keyboard, even when it is in fixed height mode.

This works on R+ only where the required API was introduced. The older
version opens the tab but does not collapse as there is no way to
detect the close event.

Bug: 1385168
Change-Id: I85feaee3b3a75fcd2157a8e3fa3da68fae4b9495
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4113802
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1085492}