[clang] [APINotes] Add SWIFT_RETURNS_(UN)RETAINED support to APINotes (PR #118938)

[Gábor Horváth via cfe-commits]

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@@ -542,6 +542,9 @@ class FunctionInfo : public CommonEntityInfo {
   /// The result type of this function, as a C type.
   std::string ResultType;
 
+  /// Swift name of this entity.
+  std::string SwiftReturnOwnership;
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Xazax-hun wrote:

We talked about this with Egor offline. I am also OK with the string approach, looks like users can already inject arbitrary `SwiftAttr` using existing annotations. So we do not open up new things. That being said, one advantage of the enum approach is that the user might get a better diagnostic when something is misspelled. 

https://github.com/llvm/llvm-project/pull/118938