Introduce Default Ime height.

Assume IME_DEFAULT_HEIGHT_DP = 300.
When ime is yet to be shown but the UI is ready, then use
IME_DEFAULT_HEIGHT_DP.

For the 2nd time onwards save the actual ime height and use it when the
keyboard is not shown yet.

Bug: 285166099
Test: Manual
Change-Id: I33e38cbd5c2910f4a6dc4cc83c8dc4b6d94fbcff