Allow to show non-current users.

- Traditionally, we only show the current user and its profile users.
  But, to support the multi-display, multi-user system, we'd like to
  show the background users too.
- This CL will replace WMS.isCurrentProfile() with UMI.isUserVisible().

Bug: 239828153
Test: atest WmTests
Change-Id: Ie432e413aab256b6bac5d4537d19bdcbb0dd8956