Utils: Extend transform for container insertion

You can now return a container and it will be appended to the result
container. That has the drawback of generating temporary container but
if we get them already it makes the code much more readable than a raw
loop.

Change-Id: Ibcd38e85ef759c18cd8da0fac0185f0f6fc123e2
Reviewed-by: Qt CI Patch Build Bot <ci_patchbuild_bot@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

tests/auto/algorithm/tst_algorithm.cpp

@@ -402,6 +402,24 @@ void tst_Algorithm::transform()
         const QHash<int, int> expected({{1, 2}, {2, 3}, {3, 4}, {4, 5}});
         QCOMPARE(trans, expected);
     }
+    {
+        // std::vector -> std::vector appending container
+        const std::vector<int> v({1, 2, 3, 4});
+        const auto trans = Utils::transform<std::vector<int>>(v, [](int i) -> std::vector<int> {
+            return {i, i * 2};
+        });
+        const std::vector<int> expected{1, 2, 2, 4, 3, 6, 4, 8};
+        QCOMPARE(trans, expected);
+    }
+    {
+        // QList -> QList appending container
+        const QList<int> v({1, 2, 3, 4});
+        const auto trans = Utils::transform<QList<int>>(v, [](int i) -> QList<int> {
+            return {i, i * 2};
+        });
+        const QList<int> expected{1, 2, 2, 4, 3, 6, 4, 8};
+        QCOMPARE(trans, expected);
+    }
 }
 
 void tst_Algorithm::sort()