Add Vector4 to VisualShader

[Geometror]

Split from #59970, this PR adds Vector4 to VisualShader without introducing a new variant type. 'Quaternion' is used to transfer data to the shader instead of 'Plane' since its internal structure is more similar to a general Vector4 type (component names: xyzw, 4 floats instead of one normal Vector3 plus the displacement component). Still feels a bit off to use a Quaternion for that, but as #59970 requires more discussion or won't be merged at all, I think its ok for now (also, it can easily be changed).

Closes godotengine/godot-proposals#3761

Detailed changes:

• Added new Vec4Uniform and Vec4Constant nodes
• Added Vector4 support to all vector operation nodes
• Implement conversion between primitive types (behavior consistent with Vector2/Vector3)
• [While at it] Fix incorrect conversion from vec2 to int

[Chaosus]

https://github.com/godotengine/godot/blob/67957f5faaeaf03e78de8eb89524d0582294750f/scene/resources/visual_shader_nodes.cpp#L2723-L2728 requires your attention - OneMinus operator does not work with Vector4 currently

[Chaosus]

https://github.com/godotengine/godot/blob/67957f5faaeaf03e78de8eb89524d0582294750f/scene/resources/visual_shader.cpp#L2679-L2680 Add BIND_ENUM_CONSTANT(VARYING_TYPE_VECTOR_4D); to generate binding

[Geometror]

@Chaosus I overlooked a few things, but they should be fixed now:

• Fixed vector functions SATURATE, ONE_MINUS, RGB2HSV, HSV2RGB (made the last two invalid for Vector4, same behavior as for Vector2)
• Fixed vector operation CROSS and REFLECT (made them invalid, since the built-in reflect function does only accept vec3, however this could be changed in another PR as reflect is defined for all dimensions in GLSL and HLSL)
• Fixed documentation

[Chaosus]

@Geometror Hmm, I think vec4 varyings does not working correctly - check it please:

[Geometror]

Missing branch in the get_port_type function used by VisualShaderNodeVaryingSetter/VisualShaderNodeVaryingGetter. Fixed now.

[Chaosus]

Everything looks correct for me for now. Thanks for this contribution, for good and qualitative work from you as usual.

[reduz]

Approach looks good to me too, fantastic work!

[Chaosus]

Thanks!