[AST] Add some 'create' factory methods

This provides consistency with other AST nodes,
and will be useful for implementing ArgumentList
construction in the future.

lib/Sema/DerivedConformanceEquatableHashable.cpp

@@ -123,7 +123,8 @@ deriveBodyEquatable_enum_noAssociatedValues_eq(AbstractFunctionDecl *eqDecl,
                                     AccessSemantics::Ordinary, fnType);
 
     fnType = fnType->getResult()->castTo<FunctionType>();
-    auto *callExpr = new (C) DotSyntaxCallExpr(ref, SourceLoc(), base, fnType);
+    auto *callExpr =
+        DotSyntaxCallExpr::create(C, ref, SourceLoc(), base, fnType);
     callExpr->setImplicit();
     callExpr->setThrows(false);
     cmpFuncExpr = callExpr;