Handle edge-to-edge for SimpleInputMethodService

As the SimpleIME is targetting the current SDK, we have to handle the
bottom insets so that the SimpleKeyboardView does not overlap with the
navigation bar area.

Flag: EXEMPT testfix
Bug: 394328311
Test: atest InputMethodServiceTest
Change-Id: Ica92b730a93bc18438c0ca7cde2af0b338b57113