[HLSL] Replace `void *` handles in HLSLExternalSemaSource with HLSLResource builtin types

[bogner]

The resource types defined by HLSLExternalSource have a handle to the resource itself. This needs to be updated to be an HLSLResource builtin type (See #90631). This means __builtin_hlsl_create_handle will need to return that type, and the array subscript operators will need to use the builtins that index into it (See #95956).

In combination with #95952 this should be sufficient for clang codegen to generate the appropriate target types for resources in DXIL.

AC:

• The resource types in HLSLExternalSemaSource are represented using an HLSLResource builtin for the handle
• AST and CodeGen tests are updated appropriately
• RWBuffer in HLSL is lowered to LLVM IR using TargetExtType