[Shader] Add support for Visual Shaders (Godot 4.6+)

[Seb105]

See godotengine/godot#116713

[Cat-Lips]

Thanks Seb. Will look into it :)

[Cat-Lips]

Done. Let me know if this works for your use case:

GodotSharp.SourceGenerators.2.7.0-260308-1524.Release.zip

(NB: Not sure why (yet), but you'll need to call .Reset() to initialise the default values if the VisualShader resource is assigned to a scene local ShaderMaterial. Seems to work without Reset if ShaderMaterial is saved as an external resource.)