Record depth/index of generic parameters.

Another baby step toward a proper canonical form for polymorphic
function types: generic parameters will eventually be uniquable by
their depth and index.


Swift SVN r7380

lib/Serialization/ModuleFormat.h

@@ -467,6 +467,8 @@ namespace decls_block {
     GENERIC_TYPE_PARAM_DECL,
     IdentifierIDField, // name
     DeclIDField, // context decl
+    BCVBR<4>,    // depth
+    BCVBR<4>,    // index
     TypeIDField, // superclass type
     TypeIDField  // archetype type
                  // Trailed by the conformance info (if any).