Map HLSL `SampleGrad` to GLSL `textureGrad[Offset]`
Map HLSL `SampleGrad` to GLSL `textureGrad[Offset]`

- This was an easy case, as far as these things go.

shader-slang/slang,csyonghe/slang,csyonghe/slang,shader-slang/slang,shader-slang/slang,csyonghe/slang