* [hlsl-out] Write `mad` intrinsic for `fma` function
- This should be enough because we only support f32 for now.
- Adds a new test for WGSL functions, in the spirit of operators.wgsl.
- Closes#1579
* Add FMA feature to glsl backend
- I think this is right. Just iterate all known expressions in all
functions and entry points to locate any `fma` function call.
Should not need to walk the statement DAG.
* Transform GLSL fma function into an airthmetic expression when necessary
* Add tests for GLSL fma function tranformation
* Remove the hazard comment from the webgl test input
* Add helper method for fma function support checks
* Address review comment
