[video_player] Add embedded cc support for video player

[mahdishahbazi3653]

Some videos like HLS includes embedded subtitle in them self. Both mobile native players (Exoplayer and AVPlayer) supports this functionality.
User now can get available subtitle option and set one of it. The video_player will stream subtitle from native to flutter video_player controller caption so we can show in flutter.

Fixed issues:

• [video_player] Support for Embedded Captions flutter#109153
• Video player plugin should support WebVTT closed captions file format.  flutter#50595

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[mahdishahbazi3653]

Closing PR Since build fails. Will send separate PR for interface, Android, iOS and video player it self

[stuartmorgan]

Please see https://github.com/flutter/flutter/wiki/Contributing-to-Plugins-and-Packages#changing-federated-plugins for our process for multi-package changes.

[hellohuanlin]

Hmmm, this work could be skipped if we migrate to platform view implementation sooner (which supports CC out of the box).

As of now we have no choice but to manually add CC labels. I saw you pushed updates. Let me know if it's ready for review.