API for IME language settings activity

Introduce a new attribute for InputMethodInfo to define an activity
for IME language settings. This activity allows users to modify the
languages (or keyboard layouts) of the IME.

Test: atest
  InputMethodInfoTest#testEquals
  InputMethodInfoTest#testInputMethodInfoProperties
  InputMethodInfoTest#testInputMethodInfoWriteToParcel
Bug: 311791923
Flag: android.view.inputmethod.ime_switcher_revamp
Change-Id: I18e7c5dc5271bee44e4540b3070b989df4e27c4c