Add FCast support for streaming to Android TVs

[paulverbeke]

Is your feature request related to a problem? Please describe.
At the moment GmsCore doesn't support Chromecast protocol V2, only V1. But since V1 is old/deprecated, all apps using microG effectively can't cast to recent/modern devices that have modern cast protocol implementations

Describe the solution you'd like
Implement the FCast protocol instead. FCast is part of the FUTO organisation and is an open-source cast implementation that supports sending to FCast, Chromecast and Airplay (V1 only for now) receivers/destinations. According to their documentation they provide SDK for sender and an application for receivers. Developers can integrate FCast support in their app using the SDK and cast to FCast supported receivers.

Despite being mentioned nowhere in their website or documentation, apparently their sender SDK also supports Chromecast receivers out of the box. It is mentioned in this video and in these issues:

• here to the Chromecast on SHIELD TV
• here to a nameless TV
• here Chromecast and Airplay v1 are mentioned

Implementing this could help YouTube Revanced and YouTube RVX (that both uses GmsCore) to make the Casting feature work.

I'm not affiliated with FUTO or FCast, I just recently discovered this in their recent video.

Thanks