Make the event.composed property in mouseenter, mouseleave, pointerenter and pointerleave events "false" to be spec compliant and to fix interop gaps. Both the UI Events spec for Mouse Events and the Pointer Events spec define these events as non-composed. Both specs switched away from their original definitions few years ago: https://github.com/w3c/uievents/pull/210 https://github.com/w3c/pointerevents/pull/461 In addition to addressing the interop gap, this change also fixes an erroneous double/triple dispatch of these events to a shadow DOM host in Chromium when the shadow DOM also listens to the event (https://crbug.com/1136584).
Docs: https://w3c.github.io/pointerevents/#attributes-and-default-actions