script: Unsilence all main thread TaskQueue errors (#34849)

No longer hide errors while queueing tasks on the main thread. This
requires creating two types of `TaskSource`s: one for the main thread
and one that can be sent to other threads. This makes queueing a bit
more efficient on the main thread and more importantly, no longer hides
task queue errors.

Fixes #25688.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Mukilan Thiyagarajan <mukilan@igalia.com>

components/script/dom/selection.rs

@@ -98,8 +98,7 @@ impl Selection {
                     this.task_queued.set(false);
                     this.document.upcast::<EventTarget>().fire_event(atom!("selectionchange"), CanGc::note());
                 })
-            )
-            .expect("Couldn't queue selectionchange task!");
+            );
         self.task_queued.set(true);
     }