script: Move TaskManager to GlobalScope (#34827)

This is a simplification of the internal `TaskQueue` API that moves the
`TaskManager` to the `GlobalScope` itself. In addition, the handling of
cancellers is moved to the `TaskManager` as well. This means that no
arguments other than the `task` are necessary for queueing tasks, which
makes the API a lot easier to use and cleaner.

`TaskSource` now also keeps a copy of the canceller with it, so that
they always know the proper way to cancel any tasks queued on them.

There is one complication here. The event loop `sender` for dedicated
workers is constantly changing as it is set to `None` when not handling
messages. This is because this sender keeps a handle to the main
thread's `Worker` object, preventing garbage collection while any
messages are still in flight or being handled. This change allows
setting the `sender` on the `TaskManager` to `None` to allow proper
garbabge collection.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/script_runtime.rs

@@ -399,8 +399,7 @@ unsafe extern "C" fn promise_rejection_tracker(
                     );
 
                     event.upcast::<Event>().fire(&target, CanGc::note());
-                }),
-                global.upcast(),
+                })
             ).unwrap();
             },
         };
@@ -455,7 +454,7 @@ unsafe extern "C" fn content_security_policy_allows(
                 global
                     .task_manager()
                     .dom_manipulation_task_source()
-                    .queue(task, &global)
+                    .queue(task)
                     .unwrap();
             }
         }
@@ -529,8 +528,7 @@ pub fn notify_about_rejected_promises(global: &GlobalScope) {
                             target.global().add_consumed_rejection(promise.reflector().get_jsobject().into_handle());
                         }
                     }
-                }),
-                global.upcast(),
+                })
             ).unwrap();
         }
     }