Feature Request: expose glslang's option to combine separate HLSL Texture*D and SamplerState objects

A while ago, GLSLang added functionality to automatically combine separate Textures and Samplers into SampledImage SPIRV objects (See this [issue](https://github.com/KhronosGroup/glslang/issues/591) and this [PR](https://github.com/KhronosGroup/glslang/pull/856)).

It would be very useful if this functionality is exposed in shaderc, as this would allow compiling HLSL shaders into an optimal SPIRV assembly without using SPIRV-cross to combine the texture and sampler objects.

I could implement this myself, if anyone can tell me what exactly I have to do to comply with section 4b) of the Apache License, which states that any modified files have to carry prominent notice. Does this apply to pull requests / forks as well?