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

Thanks @nomadsgalaxy.

xtask/src/layers.rs

@@ -36,6 +36,8 @@ impl Class {
 /// prefix.
 pub const TABLE: &[(&str, Class)] = &[
     ("geom", Class::Layer(0)),
+    // 3D mouse descriptors and reports (no workspace dependencies; the apps read the device)
+    ("space-mouse", Class::Layer(0)),
     // the derive macros (proc-macro, no workspace dependencies)
     ("derive", Class::Standalone),
     ("sketch", Class::Layer(1)),