feat(ui): offer a cube navigator alongside signed axes (#664)

Adds a View navigator preference (Navigation page) with an optional cube navigator alongside the signed axes, which stay the default (#165).

crates/ui-egui/tests/scenarios/navigation_cube_hover.json

@@ -0,0 +1,65 @@
+[
+  {"call":"ui.prefs","params":{"navigator_style":"cube"}},
+  {
+    "note": "Cube facets own one highlight at a time and choose principal views."
+  },
+  {
+    "call": "ui.view",
+    "params": {
+      "view": "home"
+    }
+  },
+  {
+    "move": {
+      "handle": "navigation_cube:top"
+    }
+  },
+  {
+    "expect": {
+      "count": {
+        "name": "axis_view_highlights",
+        "value": 1
+      }
+    }
+  },
+  {
+    "click": {
+      "handle": "navigation_cube:top"
+    }
+  },
+  {
+    "expect": {
+      "camera": {
+        "yaw_deg": 0,
+        "pitch_deg": 90
+      }
+    }
+  },
+  {
+    "click": {
+      "handle": "navigation_cube:control:down"
+    }
+  },
+  {
+    "expect": {
+      "camera": {
+        "yaw_deg": 0,
+        "pitch_deg": 0
+      }
+    }
+  },
+  {
+    "move": [
+      800,
+      500
+    ]
+  },
+  {
+    "expect": {
+      "count": {
+        "name": "axis_view_highlights",
+        "value": 0
+      }
+    }
+  }
+]