/usr/share/postgresql/10/extension/pg_visibility.control is in postgresql-10 10.6-0ubuntu0.18.04.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | # pg_visibility extension
comment = 'examine the visibility map (VM) and page-level visibility info'
default_version = '1.2'
module_pathname = '$libdir/pg_visibility'
relocatable = true
|