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_source.rs

@@ -46,6 +46,8 @@ pub(crate) enum TaskSourceName {
     Gamepad,
     /// <https://w3c.github.io/IntersectionObserver/#intersectionobserver-task-source>
     IntersectionObserver,
+    /// <https://www.w3.org/TR/webgpu/#-webgpu-task-source>
+    WebGPU,
 }
 
 impl From<TaskSourceName> for ScriptThreadEventCategory {
@@ -72,6 +74,7 @@ impl From<TaskSourceName> for ScriptThreadEventCategory {
             TaskSourceName::Timer => ScriptThreadEventCategory::TimerEvent,
             TaskSourceName::Gamepad => ScriptThreadEventCategory::InputEvent,
             TaskSourceName::IntersectionObserver => ScriptThreadEventCategory::ScriptEvent,
+            TaskSourceName::WebGPU => ScriptThreadEventCategory::ScriptEvent,
         }
     }
 }