Check the user visibility only when visible background user is enabled

In phone, it allows to add a window while a user is stopping, the new
visibility check could break this behavior, so we'd like to keep the
behavior in the device where visibile background user is disabled.

Bug: 332890402
Test: atest WmTests:WindowManagerServiceTests
Change-Id: I0b1d9460cfbab57ab06659238d97510112fff390