This adds a new boolean flag, config_show_assist_and_voice_input, which when set to false will hide the assist_and_voice_input preference item. Bug: 62379282 Test: make RunSettingsRoboTests ROBOTEST_FILTER=DefaultAssistPreferenceControllerTest Change-Id: I3bfc84f0fba07cd52679269daadbdcfccd205ff1