Detect whether overflow button should be shown based on menu key state

Some devices may have hardware keys but not contain a hardware menu key.
Hardware keys are also able to remapped. The overflow button detection logic
currently does not take that into account. This change allows detects
whether any key is capable of emitting the MENU_ACTION keystroke in
order to determine whether the overflow button should be shown or not.

Change-Id: I8699bd0242560314f8eadc54b187c69c992cf875

Conflicts:
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java
	services/java/com/android/server/wm/WindowManagerService.java