[Serialization] Serialize internal closure labels

Since 865e80f9c4 we are keeping track of internal closure labels in the closure’s type. With this change, wer are also serializing them to the swiftmodules.

Furthermore, this change adjusts the printing behaviour to print the parameter labels in the swiftinterfaces.

Resolves rdar://63633158

lib/Serialization/ModuleFormat.h

@@ -56,7 +56,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 607; // async / throws property decls
+const uint16_t SWIFTMODULE_VERSION_MINOR = 608; // internal parameter labels
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///
@@ -1007,6 +1007,7 @@ namespace decls_block {
   using FunctionParamLayout = BCRecordLayout<
     FUNCTION_PARAM,
     IdentifierIDField,   // name
+    IdentifierIDField,   // internal label
     TypeIDField,         // type
     BCFixed<1>,          // vararg?
     BCFixed<1>,          // autoclosure?