script: Include click count as the detail of mouseup and mousedown events (#41833)

This change improves the counting of clicks for mouse button events by
ensuring that `detail` property of those events includes the click
count. This `detail` differs from that of `dblclick` events where the
`detail` is always 2. In addition, it ensures that the click count can
increase for mouse buttons that do not cause `click` and `dblclick`
events (such as the right mouse button).

Testing: This change adds two Servo-specific WPT-style tests. While this
behavior is specified a bit, the details are implementation specific.

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

tests/wpt/mozilla/meta/MANIFEST.json

@@ -12919,6 +12919,15 @@
     ]
    },
    "input-events": {
+    "dblclick-events-fired-every-two-clicks.html": [
+     "9ad53ceaf05018bb48e4ff2424da4e45fbca6be6",
+     [
+      null,
+      {
+       "testdriver": true
+      }
+     ]
+    ],
     "input-events-textarea-cut-paste.html": [
      "7e1151d222b5a5210921345a3e60434194cd1794",
      [
@@ -12936,6 +12945,15 @@
        "testdriver": true
       }
      ]
+    ],
+    "mouse-button-events-detail-increases-indefinitely.html": [
+     "6bf57fe3accad4d3cbfb454e10f31b0a8540b5a5",
+     [
+      null,
+      {
+       "testdriver": true
+      }
+     ]
     ]
    },
    "mozilla": {