[HLSL] Add `AppendStructuredBuffer` and `ConsumeStructuredBuffer` definitions to HLSLExternalSemaSource

[hekota]

Add AppendStructuredBuffer and ConsumeStructuredBuffer definitions to HLSLExternalSemaSource.

AppendStructuredBuffer is a streaming output buffer:
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/sm5-object-appendstructuredbuffer

ConsumeStructuredBuffer is a streaming input buffer:
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/sm5-object-consumestructuredbuffer

AppendStructuredBuffer<float> Buf1 : register(u0);
ConsumeStructuredBuffer<float> Buf2 : register(u1);

The resource definitions will contain a handle that will be lowered to a dx.RawBuffer target extension type with scalar, vector or UDT as its type argument.

Refer to Proposal for mapping resource attributes for the attribute mapping.