[clang] [APINotes] Serialize function-like Where.Parameters (PR #204147)

[via cfe-commits]

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@@ -1043,6 +1043,22 @@ class YAMLConverter {
                          TheNamespace.Items, SwiftVersion);
   }
 
+  bool getWhereParameters(
+      const Function &Function,
+      std::optional<llvm::ArrayRef<llvm::StringRef>> &WhereParameters) {
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StoeckOverflow wrote:

Good point, I’ll switch this to return the pair and remove the out parameter. I’ll apply it in this PR as well to keep the cleanup focused here.

`FunctionWhere::Parameters` is still intentionally optional, as it distinguishes malformed `Where: {}` from valid `Where: { Parameters: [] }`. The empty list is an exact zero-parameter selector, while an empty `Where` block should be diagnosed rather than treated as that selector.

https://github.com/llvm/llvm-project/pull/204147