Add identifier to IME Switcher menu outermost view

This enables referencing the view in end-to-end tests that require
scrolling.

Flag: android.view.inputmethod.ime_switcher_revamp
Test: atest testShowInputMethodPicker testInputMethodPickerSwitchIme
  testInputMethodPickerOpenLanguageSettings
Bug: 311791923
Change-Id: I47f1a17d6850a4ca4c3e716ae012c1e80ec73669