3D mouse: any HID multi-axis controller with motion axes (#1880)

Thanks @nomadsgalaxy.

crates/space-mouse/src/lib.rs

@@ -0,0 +1,15 @@
+//! 3D mouse input that doesn't depend on how the device is read or what the motion drives. The
+//! apps open the device their own way (hidraw on Linux, hidapi on Windows), pass its report
+//! descriptor to [`Descriptor::parse`] and each input report to [`Layout::decode`], and apply the
+//! six axes and the buttons they get back to their own camera and commands.
+//!
+//! Any device that declares a HID Multi-axis Controller is read the same way: 3Dconnexion's,
+//! which send translation and rotation in two reports and their buttons in a third, and homemade
+//! ones, which often send all six axes in one report, sometimes after their buttons. The
+//! descriptor says where each axis and button is.
+#![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
+#![forbid(unsafe_code)]
+
+mod descriptor;
+
+pub use descriptor::{Descriptor, FULL_SCALE, Field, Layout, MAX_BUTTONS, Report};