Move IME Switcher Menu Settings button tests

This moves the tests related to the IME Switcher Menu Settings button
from CTS to internal tests, as there is no hard requirement on the
button being implemented as such.

Flag: EXEMPT testfix
Bug: 416313466
Test: atest InputMethodServiceTest#testImeSwitcherMenu_openLanguageSettings
  InputMethodServiceTest#testImeSwitcherMenu_noLanguageSettingsWhenScreenLocked
  InputMethodServiceTest#testImeSwitcherMenu_noLanguageSettingsWhenDeviceNotProvisioned
Change-Id: I863791a7aac524a305e1b9c433847aff12f82fe9