Add missing shader built-in overloads

[Chaosus]

No description provided.

[clayjohn]

I dont think all of the overloads you added are supported.

Here is what the spec has to say:

When the built-in functions are specified below, where the input arguments (and corresponding output) can be float, vec2, vec3, or vec4, genType is used as the argument. Where the input arguments (and corresponding output) can be int, ivec2, ivec3, or ivec4, genIType is used as the argument. Where the input arguments (and corresponding output) can be uint, uvec2, uvec3, or uvec4, genUType is used as the argument. Where the input arguments (or corresponding output) can be bool, bvec2, bvec3, or bvec4, genBType is used as the argument. For any specific use of a function, the actual types substituted for genType, genIType, genUType, or genBType have to have the same number of components for all arguments and for the return type. Similarly for mat, which can be any matrix basic type.
(pg 80 https://www.khronos.org/registry/OpenGL/specs/gl/GLSLangSpec.3.30.pdf)

step() for example has two overloads:

genType step (genType edge, genType x)
genType step (float edge, genType x)

So I don't think that the overloads added are valid.

[Chaosus]

@clayjohn Strange, they are working when testing with SHADERed and the Godot itself, this seems like a non-standard extension then? Ok, I will clean up this PR, and add some missing stuff like texture functions with Offset which GLES3 is supported.

[clayjohn]

@clayjohn Strange, they are working when testing with SHADERed and the Godot itself, this seems like a non-standard extension then? Ok, I will clean up this PR, and add some missing stuff like texture functions with Offset which GLES3 is supported.

I wonder if GLSL does an implicit type-conversion of the arguments passed into the functions. In which case, maybe we should allow them...
Edit: Looks like the compiler does an implicit conversion to the floating point equivalents, see: http://shader-playground.timjones.io/5dbb4aa04a7491496fa6fd78c04ce6fd

And for reference: GLSL 330 spec at section 4.1.10 "implicit conversions" and section 6.1 "function definitions"

[Chaosus]

I see, then I will remove that conversion overload stuff and for the future, I should probably implement that conversion implicitly.

[Chaosus]

Added packing/unpacking functions (supersedes #52767) and added functions described in https://www.khronos.org/registry/OpenGL/specs/es/3.1/GLSL_ES_Specification_3.10.withchanges.pdf (bitfieldExtract, bitfieldInsert, bitfieldReverse, bitCount, findLSB, findMSB, uaddCarry, usubBorrow)

[akien-mga]

Thanks!