OpName is only for debug information, so we must be very careful that
we do not reuse the same name for different variables.
This was previously done for local variables, but this commit extends
this to global variables as well.
Reformats the entire codebase. Better to do it now than later.
Adds .clang-format and a convenience script format_all.sh which formats
everything automatically.
Add virtual CompilerGLSL emit_sampled_image_op function for OpSampledImage.
Under MSL, set sampler ID for local OpSampledImage objects and extract it when emitting sampler.