Move click event trigger from embedding layer to ScriptThread (#36413)

1. Move click event trigger from embedding layer to `ScriptThread`
2. Previously, the logic is to trigger click event at same position as
`MouseButtonAction::Up` if `MouseButtonAction::Up` is within 10px of
`MouseButtonAction::Down`, in embedding layer. This PR ~~removes the
condition~~ moves the check to `ScriptThread`.

Testing: tested for webdriver with self written test case. Perform
actions of pointermove, pointerdown, pointerup in sequence. Click event
can now be triggered.
Fixes: #35395 

cc @xiaochengh @jdm 

For `MAYBE? TODO:` part I added, should we do it? I read the
[spec](https://w3c.github.io/uievents/#event-type-click), it doesn't
specify we have to implement MDN's way.

If we should work in the MDN's way, it also should be fixed in another
PR, as this PR doesn't regress anything. Also I am not sure what is the
best way to do it.
Should I handle it in
4d4f94936f/components/script/dom/document.rs (L1296-L1297)?

---------

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>

components/shared/embedder/input_events.rs

@@ -51,7 +51,7 @@ pub struct MouseButtonEvent {
     pub point: DevicePoint,
 }
 
-#[derive(Clone, Copy, Debug, Deserialize, Serialize)]
+#[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]
 pub enum MouseButton {
     Left,
     Middle,