Add the user switcher chip to the status bar

Add a StatusBarUserSwitcherContainer (plus a view controller) which can
show the current user information and present the user switcher when
tapped. This CL also aggregates all of the current user information into
the StatusBarUserInfoTracker so that the view controllers are
lightweight and reusable in the keyguard and unlocked statusbar.

Test: atest SystemUITests; manual
Bug: 217250837
Change-Id: I5fffb01e191d7bcd95d3a0651208bf0ca8eb45f8