oak: Hide desks widgets in partial overview

Demo: http://b/330789843#comment3
Fixed: b/330789843
Test: Added new test + manually
Change-Id: Id919fc1c10672919eae4d1ee8aba2ec22c0a27a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5403681


Commit-Queue: Michele Fan <michelefan@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280006}