Synchronize dispatch_actions in WebDriver (#36932)

Implement missing synchronization in `dispatch_actions` of `WebDriver`.
https://w3c.github.io/webdriver/#dispatching-actions

> The user agent event loop has spun enough times to process the DOM
events generated by the last invocation of the >[dispatch tick
actions](https://w3c.github.io/webdriver/#dfn-dispatch-tick-actions)
steps.

- Add a way for `ScriptThread` to notify `WebDriver` about the
completion of input commands.
- Add a `webdriver_id` field for `InputEvent`. `ScriptThread` uses it to
distinguish WebDriver events and sends notification.

Tests:
`./mach test-wpt --product servodriver -r
tests\wpt\tests\webdriver\tests\classic\element_click\events.py` pass if
`hit_testing` pass. Check
[issue](https://github.com/servo/servo/issues/36676#issuecomment-2882917136)

cc: @xiaochengh

---------

Signed-off-by: batu_hoang <longvatrong111@gmail.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/shared/constellation/from_script_message.rs

@@ -17,6 +17,7 @@ use devtools_traits::{DevtoolScriptControlMsg, ScriptToDevtoolsControlMsg, Worke
 use embedder_traits::{
     AnimationState, EmbedderMsg, FocusSequenceNumber, JSValue, JavaScriptEvaluationError,
     JavaScriptEvaluationId, MediaSessionEvent, TouchEventResult, ViewportDetails,
+    WebDriverMessageId,
 };
 use euclid::default::Size2D as UntypedSize2D;
 use http::{HeaderMap, Method};
@@ -652,6 +653,8 @@ pub enum ScriptToConstellationMessage {
         JavaScriptEvaluationId,
         Result<JSValue, JavaScriptEvaluationError>,
     ),
+    /// Notify the completion of a webdriver command.
+    WebDriverInputComplete(WebDriverMessageId),
 }
 
 impl fmt::Debug for ScriptToConstellationMessage {