Replace ACTION_USER_SWITCHED with UserTracker

ACTION_USER_SWITCHED only applies to the foreground user and will not
trigger for concurrent secondary users. By replacing this with
UserTracker, the switching logic can be modify to track what is relevant
for a given display/user.

Bug: 249831072
Test: atest SystemUIUnitTests
Change-Id: I6f5d482072ae92d7dda5e1753901b3f5dc521312