Add variant of showSystemOutputSwitcher that takes sessionToken

Apps that want to launch the media routing system output switcher from
within their app's UI can call the existing showSystemOutputSwitcher()
method. However, apps with multiple MediaSession's had no way to
indicate which session the output switcher should use, and the session
the current code picks by default might not be the one the developer
wanted to present to the user. This CL fixes that by adding a variant
of showSystemOutputSwitcher() that takes a MediaSession.Token
argument.

Bug: 402802435
Bug: 367799834
Flag: com.android.media.flags.enable_route_visibility_control_api
Test: atest OutputSwitcherTest
Change-Id: I8b4f6ec2b803d9c687a57c73206731ed012080f1