bento_bar: Ensure the bento bar is only created in ACTIVE user session

Currently, the bar might be shown on non-active user session. This is
because `ShouldPersistentDesksBarBeCreated()` does not check session
state.

Check the session state inside `ShouldPersistentDesksBarBeCreated()`,
and make sure the bar will not be created if it's not active.

Test: PersistentDesksBarTest.NoPersistentDesksBarInNonActiveUserSession
Bug: 1237502
Change-Id: I6fb1347e5cd37d18d05cb387a4a5986d41e38a84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3108458
Commit-Queue: Yongshun Liu <yongshun@chromium.org>
Reviewed-by: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/main@{#914610}