Add a meson option -Dtests and --without-tests automake option
to disable the compilation of all available testcases.
This is useful for compiling projects with Flatpak such as
GNOME Control Center which disables all possible integrations since they
only need the DBus part of ModemManager.
Contributes to https://gitlab.gnome.org/GNOME/gnome-control-center/-/merge_requests/1392
meson is a build system focused on speed an ease of use, which
helps speeding up the software development. This patch adds meson
support along autotools.