TextEditor: Dissolve QuickFixAssistProcessor

... into QuickFixAssistProcessor and QmlJSQuickFixAssistProcessor,
by essentially duplicating the class, but moving the actual work to
a new a GenericProposal::createProposal(...QuickFixOperations...)

Less indirection, and less code in total.

Change-Id: I2f8cba970bf587c9cbf04321269a60ed51bfae2a
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cppeditor/cppquickfix.cpp

@@ -52,10 +52,3 @@ void CppQuickFixFactory::matchingOperations(const QuickFixInterface &interface,
         return;
     match(*cppInterface, result);
 }
-
-QList<QuickFixFactory *> CppQuickFixFactory::cppQuickFixFactories()
-{
-    return Utils::filtered(QuickFixFactory::allQuickFixFactories(), [](QuickFixFactory *f) {
-        return qobject_cast<CppQuickFixFactory *>(f) != nullptr;
-    });
-}