QFlatMap: add an alias for using QVarLengthArrays

... in an attempt to foster the use of this data structure by making
it less onerous to spell.

Pick-to: 6.3 6.2
Change-Id: Ib9d17029c75278edde6ba90f65f68af179a6d230
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/tools/qflatmap_p.h

@@ -993,6 +993,9 @@ private:
     containers c;
 };
 
+template<class Key, class T, qsizetype N = 256, class Compare = std::less<Key>>
+using QVarLengthFlatMap = QFlatMap<Key, T, Compare, QVarLengthArray<Key, N>, QVarLengthArray<T, N>>;
+
 QT_END_NAMESPACE
 
 #endif // QFLATMAP_P_H

tests/auto/corelib/tools/qflatmap/tst_qflatmap.cpp

@@ -558,8 +558,7 @@ void tst_QFlatMap::viewIterators()
 
 void tst_QFlatMap::varLengthArray()
 {
-    using Map = QFlatMap<int, QByteArray, std::less<int>,
-                         QVarLengthArray<int, 1024>, QVarLengthArray<QByteArray, 1024>>;
+    using Map = QVarLengthFlatMap<int, QByteArray, 1024>;
     Map m{ { 2, "twee" } };
     m.insert(1, "een");
     m.remove(1);