Properly animate SIM PIN entry screen transition.

Currently, in the MSIM case, the transition between the PIN entry
screens of SIM1 and SIM2 isn't animated, leading to subpar UX. Fix this
by clearing the previously entered PIN of SIM1 in an animated way when
switching to the SIM2 PIN screen.

Change-Id: I7cb6c19590817c47950403e3022d770655ddd2ac