Set focus on the first focusable child of the form if no cursor is defined

issue4091
review7441003
Use same order for children as focus_sort_tab to find focusable child

get_children doesn't return children ordered so they must be ordered according
to their position and the direction.

issue4089
review7451002
Don't remove unmodified non-valid record from One2Many

issue4099
review5491003
Check if record is still in the multiselection when displaying

The records of current value could no more be in the selection if it has changed
because of the domain. So it must no more be displaied and it will be removed by
the call to set_client.

issue4029
review9541002