QList: use new assign() in operator=(std::initializer_list)

operator=(~) and assign(~) share similar names but, until now, have not
shared the same functionality. This patch introduces the usage of
QList::assign() within the non-sharing assignment operator to
effectively boost efficiency by reusing the available capacity.

Task-number: QTBUG-106201
Change-Id: I01a0511af336f2f410158a07d91e5759c8ff46db
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qlist.h

@@ -289,10 +289,7 @@ public:
 
     QList<T> &operator=(std::initializer_list<T> args)
     {
-        d = DataPointer(Data::allocate(qsizetype(args.size())));
-        if (args.size())
-            d->copyAppend(args.begin(), args.end());
-        return *this;
+        return assign(args);
     }
 
     template <typename InputIterator, if_input_iterator<InputIterator> = true>