Compute derivative workgroup size error checks may raise false positives

[jeffbolznv]

Thanks for merging. I just noticed that since this is doing the checks as it parses the shader, whether you get an error depends on the order of setting the derivative layout vs setting the workgroup dimensions (spec constant or not). This is a pre-existing issue and not a huge deal for me, but maybe worth fixing eventually.

Originally posted by @jeffbolznv in #3723 (comment)

[jeffbolznv]

To reproduce, just change the order of the derivative layout and workgroup size layout in the computeShaderDerivatives* tests.