Support extension KHR_fragment_shading_barycentric

[ShchchowAMD]

Add SPV support in DXC to support extension SPV_KHR_fragment_shading_barycentric.

Including new built-ins and built-in function.

Ref: https://github.com/microsoft/DirectXShaderCompiler/wiki/SV_Barycentrics

[AppVeyorBot]

:x: Build DirectXShaderCompiler 1.0.1876 failed (commit https://github.com/microsoft/DirectXShaderCompiler/commit/a3d022cdb3 by @ShchchowAMD)

[AppVeyorBot]

:x: Build DirectXShaderCompiler 1.0.1879 failed (commit https://github.com/microsoft/DirectXShaderCompiler/commit/2d47809dfe by @ShchchowAMD)

[ShchchowAMD]

Re-create to check expired build log.