Set ActivityManager to set the test callerId as the currentUserId

System headless surfaces, like auto, don't have user 0 as the current
user. In auto, test caller will be the driver, a secondary user. Setting
mock ActivityManagerInternal to set the callingUserId as the
currentUserId fix this test for auto and other headless surfaces.

Fix: 325464049
Test: atest FrameworksInputMethodSystemServerTests:com.android.server.inputmethod.InputMethodManagerServiceWindowGainedFocusTest#startInputOrWindowGainedFocus_forwardNavigation
Change-Id: I954caeb2f2bd1b9af9c7e774cd0e5ecf32f55e72