Introduce feature flag for UiAutomation inject event test/hidden APIs

UiAutomation#injectInputEvent and
UiAutomation#injectInputEventToInputFilter hidden/test API should be
deprecate in favor of UinputDevice, HidDevice, and InjectInputInProcess
for in-process input event injection.

Flag: com.android.input.flags.deprecate_uiautomation_input_injection
Test: m
Bug: 277261245

Change-Id: I4b7aacbb842b2e970df60669ef172a293dc8d04c