[clang] [HLSL] Implement `Append` and `Consume` methods on `Append`/`ConsumeStructuredBuffer` (PR #118536)

[Finn Plummer via cfe-commits]

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@@ -430,12 +432,20 @@ struct BuiltinTypeMethodBuilder {
   // Argument placeholders, inspired by std::placeholder. These are the indices
   // of arguments to forward to `callBuiltin`, and additionally `Handle` which
   // refers to the resource handle.
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inbelic wrote:

Could we add a snippet about what `LastStmtPop` denotes

https://github.com/llvm/llvm-project/pull/118536