Add API MediaRoute2Info#getProviderPackageName()

This API allows clients to obtain the provider's package name from MediaRoute2Info.

Bug: b/372908448
Test: presubmit
Flag: com.android.media.flags.enable_media_route_2_info_provider_package_name
Change-Id: Ibb14f4d65513730babf45e215057cce04448740e