Tracking issue for Spectrum support

[coderbot16]

This is a list of things needed to be fixed before Spectrum can work. Note that this is not a complete list, there might be things we don't know about. It represents a minimum of what needs to be supported as a result.

Current state on development branches:

• 1.16.x: A changing solid color screen
• 1.17.x: Fails to compile for many reasons

Needed to be fixed on all versions:

• Only 2D PNG custom textures and resource location specified custom textures are supported #1021
• Custom uniforms are not supported #1027
• Custom texture mcmeta files might only include blur, clamp, or neither, but the parser does not handle this. #1020
• shaders.properties program toggles are not supported #1026
• shaders.properties rain.depth is not supported #1028

Needed for 1.17.1+:

• Some legacy texture functions are not patched for 1.17 #1022
• gl_ProjectionMatrixInverse (and similar matrices) are not available to patched programs on 1.17+ #1023
• Sodium's imports are inserted after #extension directives when patching #1024
• Shaders that reference sampler2D texture when calling texture2D on 1.17 fail to patch properly #1025
• Custom fragment shader outputs are not supported on 1.17.1+ (needed by Nostalgia Shaders, Vanilla Plus Shaders, etc) #937