script: Ignore platform mouse move events that do not change the cursor location (#42034)

winit on macOS seems to send a mousemove event right before mouse button
up events. This interferes with interactive use of text boxes -- for
instance double-clicking to select the hovered word. This change makes
it so
that mouse move events that do not change the cursor location are
ignored.

Testing: This change adds a Servo-specific WPT-style test.

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

tests/wpt/mozilla/meta/MANIFEST.json

@@ -13016,6 +13016,15 @@
        "testdriver": true
       }
      ]
+    ],
+    "spurious-mouse-move-events.html": [
+     "9cfa22aaf90a0d3399fd03a80aa87dd0f16f76d6",
+     [
+      null,
+      {
+       "testdriver": true
+      }
+     ]
     ]
    },
    "mozilla": {