Add a new QtInstanceTreeIter struct as the weld::TreeIter
implementaton for QtInstanceTreeView.
It uses the QModelIndex of the item it points to.
Add QtInstanceTreeView::modelIndex helper methods
to convert both, an int row index and a QtInstanceTreeIter
to a QModelIndex.
This can be used to deduplicate code when (re)implementing
the methods that have two variants that either take an
int row index or a TreeIter input param.
For QtInstanceTreeView::get_id, add a new variant that
takes a QModelIndex and move the existing logic from
the implementation for the int param there and reuse
it to implemetnat the variant taking a TreeIter param
as well.
Implement a few more methods taking or returning
a weld::TreeIter.
Change-Id: I0508ad14a43214faccc6a3cba208400031bb231c
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/178069
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
aad48b06e7