snap-group: Windows visibility on desks switching

This cl fixed the windows visibility issue when switching desks.
`IsVisible()` is used in `ScopedOverviewHideWindows` when storing
window visibility in `window_visibility_` map which may not be
accurate when switching desks. Windows belong to inactive desks
will have `IsVisible()` as false. We should use `TargetVisibility()`
that returns the actual window's target visibility.

Demo: http://b/335477702#comment2
Fixed: b/335477702
Test: Added new unit test(fail w/o changes) + manually
Change-Id: I9760d5cd3c20f9836f8eed4563ffe44362ae4115
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5499107
Commit-Queue: Michele Fan <michelefan@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1294406}