[clang] [clang][ssaf] Implement JSONFormat (PR #180021)

[Balázs Benics via cfe-commits]

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@@ -29,6 +29,7 @@ class EntityIdTable;
 /// \see EntityIdTable
 class EntityId {
   friend class EntityIdTable;
+  friend class SerializationFormat;
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steakhal wrote:

So what made me thinking is that you added this friendship, but you didn't add anything to the `PrivateFieldNames.def`, and then I realised that this branch is out of date of llvm/main., and here we have our hand-rolled getters.

https://github.com/llvm/llvm-project/pull/180021