Integrate crates that will never be used outside servo into the repository

[mrobinson]

The recent euclid and ipc-channel upgrades and the upcoming webrender upgrade show how difficult it is to orchestrate dependency upgrades between these projects. Integrating these crates into the repository will make things much easier and allow us to use workspace dependencies to more easily keep dependencies up-to-date.

Here's a list of projects that should likely be integrated into the servo repository:

• https://github.com/servo/webxr
• https://github.com/servo/media
• https://github.com/servo/devices
• https://github.com/servo/fontsan