Finish the integration of webxr into the Cargo workspace (#35229)

- Run `cargo fmt` on `webxr` and `webxr-api`
- Fix clippy warnings in the existing `webxr` code
- Integrate the new crates into the workspace
- Expose `webxr` via the libservo API rather than requiring embedders to
  depend on it explicitly.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/shared/webxr/util.rs

@@ -1,8 +1,11 @@
-use crate::FrameUpdateEvent;
-use crate::HitTestId;
-use crate::HitTestSource;
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
 use euclid::Transform3D;
 
+use crate::{FrameUpdateEvent, HitTestId, HitTestSource};
+
 #[derive(Clone, Copy, Debug)]
 #[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
 pub struct ClipPlanes {