Add MediaRouter2 method to show the SystemUI output switcher

Change the way to invoke media output switcher from an intent action
handled by SystemUI to a platform api that validate the calling package
name through the binder call.

Bug: 258532462
Test: Using androidx sample app.
Change-Id: I75e0856c18b3caed5ef0ebc9a057290c9a79e1d3
4 files changed