[Flock][Feature] - Support for Video Textures

[jezell]

Flutter Issue Ticket Link:

flutter/flutter#150592

Why didn't Flutter implement this?

Many people on the team seem to think the video_player package is enough and don't understand that the video_player package is too high level to be useful for many scenarios. WebRTC for example is a scenario where you need a video texture, but you can't use the video_player package at all.

Why does this belong in Flock?

To get video to perform well, hooks are needed in the engine. At the moment, video_player_web only supports rendering video with a platform view for example. I contributed changes to the engine such as this which can be used to render video textures more efficiently:

flutter/engine#53483

But the code to grab the frames and render them is tightly coupled to the engine implementation and the best way to implement video textures has varied from release to release depending on the APIs available. Ideally, plugin authors that need video support would have a higher level primitive in the engine itself for rendering a native video source into a texture that can then be referenced with the existing Texture APIs.

Describe the solution you'd like

There are already APIs for rendering textures in Flutter, they could be a potential way to expose this. The blocker on web is that there is not currently a Texture / TextureRegistry equivalent. Adding a TextureRegistry to web would be the first step to exposing a higher level platform specific APIs that render video content into a Texture, which can then be used by the widgets that already exist to render the texture.

#45

Additional context
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