fdo#75757 remove inheritance from std::vector

Removing TextLines class by the way

Change-Id: Ic491af976d61cac8e4b37857ff3a76570611d90d
Reviewed-on: https://gerrit.libreoffice.org/12474
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>