[Development] Qt6 source changes

[Kevin Kofler]

Thiago Macieira wrote:
> We're studying what to do with QList, but the idea is that the name
> "QList" will be completely ok and identical to QVector. The technical
> mechanism is in flux.

That means you will be pessimizing element inserts and removals from O(n) to 
O(mn), where n is the length of the list and m the size of each element, 
without offering a good alternative without that pessimization (sure, you 
can use a QVector<T*> or QVector<SomeSmartPointer<T>>, but those have 
somewhat different semantics and less convenient syntax).

It won't make a difference for implicitly-shared objects (but QList already 
works like a vector for those anyway), but for large in-place objects, it 
can make a big difference.

        Kevin Kofler