AST: Move a few methods from VarDecl down to ParamDecl

lib/Sema/PCMacro.cpp

@@ -477,7 +477,7 @@ public:
     }
 
     VarDecl *VD =
-        new (Context) VarDecl(/*IsStatic*/false, VarDecl::Specifier::Let,
+        new (Context) VarDecl(/*IsStatic*/false, VarDecl::Introducer::Let,
                               /*IsCaptureList*/false, SourceLoc(),
                               Context.getIdentifier(NameBuf),
                               TypeCheckDC);