feature (Texture): Add Source class

[0b5vr]

Why

To catch up with r138 changes

What

Added Source class that is going to be introduced in r138.

I also added a test code textures-source.ts .

See: mrdoob/three.js#22846
See: mrdoob/three.js#23419

Points need review

• I have very low confidence about the signature of Source.data and Texture.image
  • @Mugen87 would you mind reviewing this?
    I don't fully understand how Source works with video textures, compressed textures, ...
  • I decided to make it any for now.
• Is it reasonable to define a type SourceData ?

Checklist

• Checked the target branch (current goes master, next goes dev)
  • It's a r138 change
• Added myself to contributors table
• Ready to be merged

[0b5vr]

considering having <TSource = any> generics on Texture and Source......
I should do this in a separated PR.

Let me make a PR using any for this one.

[joshuaellis]

Great work adding a test!