Macos space mouse support (#1815)

Thanks @NecroKote.

xtask/src/layers.rs

@@ -40,6 +40,8 @@ pub const TABLE: &[(&str, Class)] = &[
     ("space-mouse", Class::Layer(0)),
     // the derive macros (proc-macro, no workspace dependencies)
     ("derive", Class::Standalone),
+    // the 3Dconnexion driver's client API on macOS (no workspace dependencies)
+    ("3dx-client", Class::Standalone),
     ("sketch", Class::Layer(1)),
     ("kernel", Class::Layer(1)),
     ("render", Class::Layer(1)),