docs: Clarify Efl.Ui.Win exit_on_close methods
exit_on_close and exit_on_all_windows_closed deserve a bit of clarification
since they have very similar meanings.
Also, add proper Eina.Value doc references.
Ref T7717
Reviewed-by: Marcel Hollerbach <mail@marcel-hollerbach.de>
Differential Revision: https://phab.enlightenment.org/D8511