fdo#75256 Improve sifr icontheme

Modify insertannotation, new minus and plus for the sidepanel, rename upperline to overline

Change-Id: Idd3de965cb6be307bf3e8326b854084ad1a7c0af
Reviewed-on: https://gerrit.libreoffice.org/12465
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>