🐃 Add buffer texture

[paulcscharf]

✨ What's this?

• Refactors texture uniforms with shared base class
• Adds buffer texture
• Fixes texture targets being mutable, which I believe to be invalid (breaking change)

🔍 Why do we want this?

Buffer textures allow for easily pushing large amounts of unstructured binary data for efficient use in shaders.

🏗 How is it done?

See by commits if you like.

💥 Breaking changes

Making the texture targets immutable is strictly speaking a breaking change.
However, the argument was already optional, and only used in a single example I'm aware of, where it passed the default value anyway.
Because of that, I consider this largely breaking on a binary level, but not code level.

If you want me to split out a separate PR, I'll do so, but I believe the change to be small enough to include here.

🔬 Why not another way?

Shader Storage Buffer Objects are even more flexible, but only supported from OpenGL 4.3 onwards, and not available on MacOS.