servo: Merge #12404 - Clean up task sources and make all tasks cancellable (from cbrewster:task_source_cleanup); r=asajeffrey

<!-- Please describe your changes on the following line: -->
This makes it so each task is a thin wrapper over a runnable and whenever a task is queued, it is automatically wrapped by the window's `runnable_wrapper`.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix  #11703 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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Source-Repo: https://github.com/servo/servo
Source-Revision: 3011d4b450b107f87fab54f6c59245ac1478fa79

servo/components/script/dom/htmlinputelement.rs

@@ -577,7 +577,8 @@ impl HTMLInputElementMethods for HTMLInputElement {
             &self.upcast(),
             atom!("select"),
             EventBubbles::Bubbles,
-            EventCancelable::NotCancelable);
+            EventCancelable::NotCancelable,
+            window.r());
         self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
     }
 
@@ -1070,7 +1071,8 @@ impl VirtualMethods for HTMLInputElement {
                                     &self.upcast(),
                                     atom!("input"),
                                     EventBubbles::Bubbles,
-                                    EventCancelable::NotCancelable);
+                                    EventCancelable::NotCancelable,
+                                    window.r());
                             }
 
                             self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);