Improvements to video players

[MrWardKKHS]

Various improvements to the two Video Players Views in the experimental module. The ultimate goal here would be to have an easy to use class that can load a video and play it, esp as a cutscene. This PR gets closer even though it still doesn't feel solved.

• The opencv video player and video player view is exposed to users now,
• The ability to loop the cv2 player added
• The default behavior of the cv2 player to resize the window turned off
• Video added from pexels https://www.pexels.com/license/
• Typing improvements

Future improvements might be to merge VideoPlayerView and CV2PlayerView as this seems like duplication

[einarf]

If we're adding mp4 file to arcade we should also add the extension here so it's included in the wheel / source distribution.
https://github.com/pythonarcade/arcade/blob/development/MANIFEST.in

[pushfoo]

I think this is good overall, but there some unresolved questions as well as a few changes which I think would be a good idea.

[pushfoo]

I'm fine with this if einarf & CI are. The MANIFEST.in addition is very good attention to detail. 👍