Resolves: fdo#71616 Elements dock: Better display of scalable braces

Change-Id: I2255be738aa2230b4102030891026f1f9ad2c38f
Reviewed-on: https://gerrit.libreoffice.org/9525
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>