Remove InputManager#getInstance

Replace all instances of InputManager with instances of InputManagerGlobal.
Add the context field in InputManager.
All methods previously accessed through instances of InputManager
have been refactored to be accessed through InputManagerGlobal, which is
a singleton class.
The SystemServiceRegistry no longer returns an instance of InputManager.

Bug: b/267758905
Test: Pre-submit
Change-Id: I2f3db1f5f4e27be9eb11d0d307aaee16a33f014d