Measure and optimize IMF latency 6/n

Few low-hanging optimizations to improve IMF latency:
- Remove duplicate call to setImeWindowStatus when showWindow() is
called from showSoftInput() already.
- Remove redundant fancy animations preference check. IME window
animation is controlled by client.
- Cache mShowImeWithHardKeyboard early on.
- Remove rendundant removeOnComputeInternalInsetsListener() when called
from onCreate().

Refer to design doc in bug for amount of latency improvements caused by
this CL.

Bug: 167947940
Bug: 167948123
Test: atest CtsInputMethodTestCases
Change-Id: I0b0750f146634d8e90e0b0ac46e9208675626d0a