Add timeouts to animations in UserSwitchingDialog.

Otherwise, onAnimationEnd callbacks are not called if the device
screen is off, and causes the user switch to flow to be blocked.

Bug: 279561434
Bug: 279819448
Test: atest UserLifecycleTests
Change-Id: Ib61df713b04b4f0b19c3f717c15a78368e0b1bdc