Structured buffers

[bogner]

• [HLSL] Add StructuredBuffer definition to HLSLExternalSemaSource llvm-project#106189
• [HLSL] Add RWStructuredBuffer definition to HLSLExternalSemaSource llvm-project#112775
• [HLSL] Add RasterizerOrderedStructuredBuffer definition to HLSLExternalSemaSource llvm-project#112776
• [HLSL] Add AppendStructuredBuffer and ConsumeStructuredBuffer definitions to HLSLExternalSemaSource llvm-project#112777
• [HLSL] Implement Load method and operator[] on structured buffers llvm-project#112977
• [HLSL] Implement Append and Consume on Append/ConsumeStructuredBuffer llvm-project#112968
• [DirectX] Introduce llvm.dx.rawBufferLoad/Store and lower them to rawBufferLoad/Store dxil ops llvm-project#106188
• [DirectX] Replace accesses to RawBuffer via getpointer with loads and stores llvm-project#121714
• [DirectX] Implement shader flag analysis for EnableRawAndStructuredBuffers llvm-project#122663