QList: support move-only types

Although it's possible to construct a QList with move-only element types, it's not usable, since most of the operations on a QList require its elements to be copyable, even if they have overloads taking rvalue refs, and no copying is done in practice (this is because QArrayDataPointer internally does a runtime check, to decide if copy or move operations should be used, see e.g. https://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/tools/qarraydatapointer.h?h=6.4.0#n225). For example: 

QList<std::unique_ptr<int>> list; // Ok
list = std::move(anotherList); // Ok

list.push_back(std::move(ptr); // Doesn't compile
l.emplace_back(new int (5)); // Doesn't compile
list.removeAt(0); // Doesn't compile
list.reserve(); // Doesn't compile
// etc.

As far as I understand, the main limitation is that QList (and other Qt containers) is designed to support implicit sharing. However, QList with move-only elements can't be copied in any case, so no implicit sharing should be required. If we disable implicit sharing for a QList with move-only element types at compile time, it should be possible to support move-only types.