Use KHR_parallel_shader_compile extension

[lgharibashvili]

At the moment compiling large shaders may freeze browser window because of blocking operation.

It would be great if it was possible to use KHR_parallel_shader_compile extension, which allows checking compilation status without blocking runtime.

More info:
https://developer.mozilla.org/en-US/docs/Web/API/KHR_parallel_shader_compile