Fullscreen user switching dialog with animations.

Instead of freezing the screen during the user switch, with this CL
we are introducing a full screen user switcher, which is showing
target user's user name and profile photo with an animated spinner
around it.

Steps of a user switch:
1. 300ms - dialog show animation
2. 500ms - spinner animation around profile picture
3. Do the actual user switch
4. 300ms - dialog dismiss animation
5. End user switch (call UserSwitchObservers.onUserSwitchComplete, and
   send ACTION_USER_SWITCHED broadcast)

Changes:
* Step1 was already there.
* Step2 is added between 1-3, which shows a nice smooth progress
  animation around profile picture, but increases the user switch
  duration by 500ms.
* Step5 and Step4 were running at the same time before, now Step5 is
  postponed after the completion of Step4. Otherwise, dismiss
  animation becomes jerky. It was also jerky with unfreezing the
  screen, now that jerkiness is gone.
* All animations are disabled for slower devices.
  see: ActivityManager.isLowRamDeviceStatic()

Results:
* We're increasing the user switch duration by 800ms. (Step2 + Step4)
* We've a full screen user switcher with smooth animations.
* There is no more jerkiness in any stage (showing, during, hiding) of
  the dialog.

Notes:
* Our intention was to run Step2 and Step3 simultaneously but it makes
  the spinner animation jerky.
* We're disabling the dialog show/hide and spinner animations when
  running UserLifecycleTests.

Bug: 269237775
Bug: 223090747
Test: atest FrameworksServicesTests:UserControllerTest
Test: atest UserLifecycleTests
Change-Id: I5e0132e19c8da25438c5dbfecdeddf475b18f7d4