Create android.view.input

This creates a new package android.view.input.
I will add more input compatibility related code here, and as a first
step this moves LetterboxScrollProcessor there.

Bug: 369865835
Test: LetterboxScrollProcessorTest, InputEventCompatProcessorTest
Flag: EXEMPT refactor
Change-Id: Ie5769e81549443b6df5cd042032430dd54906c93