[Sema]: Add Codable synthesis for enums with associated values (#34855)

* [Sema]: Add Codable synthesis for enums with associated values

* Incorporate review feedback for enum Codable synthesis

* Implement enum specific versions of existing Codable tests

* Encode parameterless enum cases as

* Add test for overloaded case identifiers

* Align code generation with latest proposal revision

* Put enum codable derivation behind flag

* clang-format sources

* Address review feedback and fix tests

* Add diagnostic for conflicting parameter identifiers

* Restructure code after rebase

lib/Frontend/CompilerInvocation.cpp

@@ -388,6 +388,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.EnableExperimentalFlowSensitiveConcurrentCaptures |=
     Args.hasArg(OPT_enable_experimental_flow_sensitive_concurrent_captures);
 
+  Opts.EnableExperimentalEnumCodableDerivation |=
+      Args.hasArg(OPT_enable_experimental_enum_codable_derivation);
+
   Opts.DisableImplicitConcurrencyModuleImport |=
     Args.hasArg(OPT_disable_implicit_concurrency_module_import);