[HLSL2021] Disallow bitfields and annotations

[llvm-beanz]

This change makes mixing bitfields and HLSL annotations an error. Since the syntax for HLSL annotations and bitfields are ambiguous, this change works around some issues with the ambiguity by disallowing mixing the two on the same declaration.

Fixes #4686

[llvm-beanz]

@microsoft-github-policy-service agree company="Microsoft"

[AppVeyorBot]

:x: Build DirectXShaderCompiler 1.0.2112 failed (commit https://github.com/microsoft/DirectXShaderCompiler/commit/743fe05512 by @llvm-beanz)

[AppVeyorBot]

:white_check_mark: Build DirectXShaderCompiler 1.0.2113 completed (commit https://github.com/microsoft/DirectXShaderCompiler/commit/05e51364c3 by @llvm-beanz)