It's used as the result in some cases. However, it's not tracked in some cases when touching the DOM. This modifies the API of `AutoTrackDOMPoint` to flush the tracking point but can keep tracking. We should use the new API in every place later. (This manually merges `WhiteSpaceVisibilityKeeper.cpp` because ESR140 still has the pref to take the legacy mode back and that blocks applying the patch cleanly.) Differential Revision: https://phabricator.services.mozilla.com/D270643