udevadm: allow a .device unit to be specified for query and trigger

udevadm: allow a .device unit to be specified for query and trigger

This is convenient when working with device units in systemd. Instead of
converting the systemd unit name to a path to feed to udevadm, udevadm
info|trigger can be called directly on the unit name.

The man page is reworked a bit to describe the modern syntax with positional
arguments first. It's just simpler to use than the positional options.