QList::insert() should never need to call a destructor. This
requires that we construct the new items in the list in order
and increment the size each time we constructed a new item.
Not having a code path that potentially calls destructors should
avoid the generation of lots of additional code for those
operations. In addition, the forward and backwards code paths
are now unified and only require somewhat different setup of
some variables at the start.
This gives us strong exception safety when appending one item,
weak exception safety in all other cases (in line with std::vector).
Change-Id: I6bf88365a34ea9e55ed1236be01a65499275d150
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
168772fe8f