Let `SdrPage::createAnnotation` et al. return the newly
created annotation rather than using an out parameter,
which makes this more straightforward.
Change-Id: Iee0561859756522ef33680c2cc9b492541a31d5e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/167019
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
b7ba358d48