[API change] Add setInvocationEffectEnabled(boolean) function to...

...VoiceInteractionService

This API enables the default assistant to enable the invocation effect:
go/floaty_invocation_effect
This is a public API intended for 2025Q4 release.

Bug: 416136399
Flag: android.service.voice.flags.set_invocation_effect_enabled_api
Test: VoiceInteractionServiceTest
Change-Id: Iaf853e9b416b61e35cd96aa0f8080eb41920eebc