[Development] Qt6 source changes

[Ulf Hermann]

> Depends on usage.
> 
> See e.g. 551efd91990e07902e5324f720cf5585865c323d
> 
>     QmlProfiler: Use QList for QmlRange container when loading .qtd
>      
>     As we are using this as a queue, with many calls to takeFirst(), a
>     QVector is prohibitively expensive here.

I should have used QQueue there, and that will hopefully still be a 
linked(-ish) list in Qt6. Or it might become a ring buffer, but please 
not a plain vector.

If we don't want to keep QQueue, I will still have the option to use an 
equivalent std container there (+/- implicit sharing).

Ulf