Animate IME with zero insets

When IME has zero insets, it doesn't map to any side and doesn't have
can't be animated.
IME can have zero insets in following cases:
1. Floating IME
2. Fullscreen IME (in landscape)
3. IME doesn't overlap with IME target window.

In order to animate a type, it must have insets. We can animate IME
from negative insets to zero and vice-versa. This makes zero insets IME a
special case of ISIDE_BOTTOM.
Deprecate SIDE_FLOATING because it shouldn't logically map to a side.

Fix: 153909316
Test: atest WindowInsetsAnimationImeTests#testZeroInsetsImeAnimates
Change-Id: I6d1d3430888db4632cb2f93e9042f692b35ebaeb