iwd: P2P support

This mostly adds the NMDeviceIwdP2P class and supporting code and basically enables gnome-network-displays to work against the IWD backend, although with a small change for which I submitted an issue to that project. It also won't actually work with IWD's NetworkConfigurationEnabled option, which is always enabled for P2P (where IWD obtains the IP config details, runs DHCP etc.), some work has been done to support this but isn't finished yet. It was enough for me to be able to test the code though.

Note it looks like the clang formatter isn't indenting this line correctly: balrog-kun/NetworkManager@50bada3c Also NM's clang-format config apparently breaks with clang-format-13, I needed to revert to clang-format-12 after an upgrade.