This is libgudev, a library providing GObject bindings for libudev. It used to be part of udev, then merged into systemd. It's now a project on its own.
The official download locations are: http://download.gnome.org/sources/libgudev
The official web site is: https://gitlab.gnome.org/GNOME/libgudev/
libgudev uses meson as its build system, so generic installation instructions apply to installing libgudev.
libgudev requires libudev (part of systemd), glib, and pkg-config. Refer to
the meson.build file itself for up-to-date version requirements.
libgudev also optionally uses umockdev for its tests.
Bugs and patches can be contributed on the project's GitLab page.
libgudev, as a combined works, is released under the GNU Lesser General
Public License version 2.1 or later. See COPYING file for details.