fdo#43494 Allow UI scaling up to 400%

Change-Id: Ibf53276b567b0591f9635f49761784900faae816
Reviewed-on: https://gerrit.libreoffice.org/6891
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>