[HLSL] Implement `Append` and `Consume` on `Append`/`ConsumeStructuredBuffer`

[hekota]

Use existing clang builtins __builtin_hlsl_buffer_update_counter and __builtin_hlsl_resource_getpointer to implement the Append method on AppendStructuredBuffer and Consume method on ConsumeStructuredBuffer.

These builtins would be lowered to appropriate LLVM DirectX intrinsics during clang codegen.
Depends on #92147 and #106188.

https://godbolt.org/z/qKGdYj5zj

struct MyStruct {
    float4 a;
};

AppendStructuredBuffer<MyStruct> AB;
ConsumeStructuredBuffer<MyStruct> CB;

[numthreads(4,1,1)]
void main() {
  MyStruct val = CB.Consume();
  AB.Append(val);
}

Docs:
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/sm5-object-appendstructuredbuffer-append
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/sm5-object-consumestructuredbuffer-consume

AC:

• Append/Consume methods are added to the AppendStructuredBuffer/ConsumeStructuredBuffer using the builtins
• Tests added