fdo#80536 UI: Menu entry for 'Edit File' -> 'Edit Mode'

In this commit not only a menu entry is created, also the name is changed
from 'Edit File' to 'Edit Mode'.

Change-Id: Icd7998307cb0337dd2ee95b298452557ab37375b
Reviewed-on: https://gerrit.libreoffice.org/10211
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>