sd-bus: set per-bus attach flag requirement mask to ANY

On the system and user busses we create it's the receiver that chooses
which metadata is attched, not the sender, hence set the requirement
mask to ANY, to allow any current of future credential bit to be
attached.
sd-bus: don't clobber return values on failure in bus_kernel_open_bus_fd()
bus-kernel: when installing an activator, ask for any kind of metadata to be attached to incoming messages

We don't know what the activated service might want in the end, hence
enable everything current and future, just to be sure.
update TODO
udevadm: split out find_device helper

The idea is to unify the way that devices can be specified.
udevadm trigger: allow matching by device name

This makes udevadm trigger mirror udevadm info, except that multiple
device names can be specified. Instructions in 60-keyboard.hwdb should
now actually work.

udevadm(8) is updated, but it could use a bit more polishing.

https://bugs.freedesktop.org/show_bug.cgi?id=82311