Update UserTracker.Callback after registering it

A user change may have already happened before the callback is
registered, which would leave the rest of WMShell with the incorrect
current user.

Additionally, ShellController now tracks the current user/profiles to
prevent it from updating UserChangeListeners when the user did not
really change. It also immediately updates new UserChangeListeners with
the current user/profiles, which removes the burden Shell classes have
of checking for user-changes that happen between their constructor and
onInit.

In the future, Shell classes should be migrated to rely solely on
UserChangeListener to keep their userId updated, or they can peek into
ShellController if they only need it in response to other events and
don't need to do work on user changes or maintain their own
currentUserId.

Flag: com.android.wm.shell.fix_missing_user_change_callbacks
Bug: 404251029
Test: adevice update, verify through logs WMShell classes always get an
update with the current user after WMShell.start()

Change-Id: I03e6c2cbcda498be786899e0d0271e98b421477e