TextEditor: Add a convenience overload for RefactoringFile::apply()

... and make use of it.
In most contexts, apply() immediately follows setChangeSet(), so
combining the two can save a lot of code on the call site.

Change-Id: I421001bd47000cb64678a57b19760becf59a4863
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/qmljseditor/qmljswrapinloader.cpp

@@ -146,8 +146,7 @@ public:
                                                       "    id: %2\n"
                                                       "    sourceComponent: %1\n"
                                                       "}\n").arg(componentId, loaderId));
-        currentFile->setChangeSet(changes);
-        currentFile->apply();
+        currentFile->apply(changes);
     }
 };