backend/native: Add udev rule to ignore vkms devices
Virtual Kernel Mode Setting (vkms) is a virtual /dev/dri/card* device not backed by any actual hardware. It's intended for testing purposes, e.g. to run tests suites with a reproducable setup, or in continuous integration pipelines.
Currently mutter don't have any tests that can run on top of vkms, but will eventually get that. To prepare for the ability to do that, and having said kernel module loaded without causing wierd issues with any active session, add an udev rule that tells mutter to ignore any vkms device.
Otherwise, when vkms is loaded, mutter would detect it, assume it's a regular monitor, configure it as such, thus add a region of the stage that ends up nowhere, which isn't very helpful. It might also conflict with running actual tests that need to interact with vkms if the active session has taken control of it.
I don't expect we get any actual vkms based testing before GNOME 40, but definitely during the GNOME 41 cycle, so to make that less painful, consider this a preparation for the "developer experience" for having vkms loaded.