[BUG] GlslEs300 Compute shaders require es profile with version 310 or above

[thargy]

After adding more automated backend testing I received the following error on compiling a compute shader across all backends:

ERROR: #version: compute shaders require es profile with version 310 or above, or non-es profile with version 420 or above

Currently the GlslEs300 backend doesn't check to see if the function is a compute shader when compiling.

[thargy]

I've added a check which fixed this issue.