QArrayDataOps: fix QList range ctors with mixed value_type in C++20 builds

The QList<X> range ctor is supposed to accept iterators with
value_types convertible to X, e.g. tst_qitemselectionrange passes
iterator to a container of QModelIndex to the ctor of a
QList<QPersistentModelIndex>. But copyAppend() is not a template, so
trying to pass QModelIndex* when QPersistentModelIndex* is expected
errors out.

Fix by taking the copyAppend() path only if the types match.

Amends 507be11303.

Change-Id: I5e3ff84a80dc05dafde5572463b33df9002c8fe0
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>

src/corelib/tools/qarraydataops.h

@@ -912,10 +912,17 @@ public:
         Q_UNUSED(distance);
 
 #if __cplusplus >= 202002L
-        if constexpr (
-            std::is_convertible_v<
+        constexpr bool canUseCopyAppend = std::conjunction_v<
+                std::is_convertible<
                     typename std::iterator_traits<It>::iterator_category,
-                    std::contiguous_iterator_tag>) {
+                    std::contiguous_iterator_tag
+                >,
+                std::is_same<
+                    std::remove_cv_t<typename std::iterator_traits<It>::value_type>,
+                    T
+                >
+            >;
+        if constexpr (canUseCopyAppend) {
             this->copyAppend(std::to_address(b), std::to_address(e));
         } else
 #endif