[HLSL] Add `RWStructuredBuffer` definition to HLSLExternalSemaSource

[hekota]

Add RWStructuredBuffer definition to HLSLExternalSemaSource.

The RWStructuredBuffer is a read-write buffer of user defined types (UDTs).
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/sm5-object-rwstructuredbuffer

The resource definition will contain a handle that will be lowered to a dx.RawBuffer target extension type with the UDT as its type argument.

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

Check that the current implementation of StructuredBuffer matches the latest proposal for the attribute mapping.