/lib/partman/visual.d/15size is in ubiquity 18.04.14.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | #!/bin/sh
. /lib/partman/lib/base.sh
cd $1
num=$2
id=$3
size=$4
type=$5
fs=$6
path=$7
name=$8
printf "\${!ALIGN=RIGHT}%s" "$(longint2human $size)"
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