Move IME MenuItem list creation in Menu Controller

This moves the mapping of ImeSubtypeListItem to MenuItem to
Menu Controller, containing the menu item type to this scope.

Additionally follows up with some cleaning in the menu controller by
extracting updateLanguageSettingsButton as a separate method.

Flag: EXEMPT refactor
Bug: 369120217
Test: atest testInputMethodPickerShownItems
  testInputMethodPickerSwitchIme
  testInputMethodPickerOpenLanguageSettings
  testInputMethodPickerNoLanguageSettingsWhenDeviceNotProvisioned
Change-Id: Icb3fa967ebddbbb02c155f26ccd2f026f97e2cde