Don't show IME Switcher settings button if locked

While the screen is locked, pressing on the settings button from the IME
Switcher menu has no effect, as we cannot launch the IME settings app in
that state. This removes the button if the screen is locked.

Flag: EXEMPT bugfix
Test: atest InputMethodManagerTest#testInputMethodPickerNoLanguageSettingsWhenScreenLocked
Bug: 397612817
Change-Id: I48816c18986e0202e4be415467a9101caa7469b3