tst_containerapisymmetry: use an algorithm

In preparation for the next changes.

Change-Id: Ibe0635dfa040842073749aa3e2ae140f27dc983a
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/corelib/tools/containerapisymmetry/tst_containerapisymmetry.cpp

@@ -608,9 +608,9 @@ template <typename Container>
 Container make(int size)
 {
     Container c;
-    int i = 1;
-    while (size--)
-        c.push_back(typename Container::value_type(i++));
+    c.reserve(size);
+    using V = typename Container::value_type;
+    std::generate_n(std::inserter(c, c.end()), size, [i = 1]() mutable { return V(i++); });
     return c;
 }