webgpu: Add the dedicated WebGPU task source (#39020)

According to the WebGPU specification there are the dedicated task
source
which is used to queue a global task for a GPUDevice on content
timeline.
https://gpuweb.github.io/gpuweb/#-webgpu-task-source

Tasks on content timeline:
- to fire "uncaptureevent" event
- to resolve GPUDevice.lost promise

Also fixed the "isTrusted" attribute status (false -> true) of the
"uncaptureevent" event by using non JS version of event dispatching.

Testing: No changes in WebGPU CTS expectations
- webgpu:api,operation,uncapturederror:*
- webgpu:api,operation,device,lost:*
- webgpu:api,validation,state,device_lost,destroy:*

Signed-off-by: Andrei Volykhin <volykhin.andrei@huawei.com>
Co-authored-by: Andrei Volykhin <volykhin.andrei@huawei.com>

components/script/task_manager.rs

@@ -153,4 +153,5 @@ impl TaskManager {
         intersection_observer_task_source,
         IntersectionObserver
     );
+    task_source_functions!(self, webgpu_task_source, WebGPU);
 }