Implement smooth FAB animations for displacement due to IME visibility changes

For the FAB to remember where it was before being displaced by an IME,
it needs to avoid persisting its position (updating the internal percentage-position value)
This change adds a parameter to onPositionChanged(), as well as our spring animation functions,
that controls whether they persist the position,
allowing us to use them for handling IME displacement.

Bug: 281150010
Test: adb sync system_ext && adb shell stop && adb shell start
Change-Id: Ic259db5d2612737aada2dd0440efce661754677b