Pass HybridEventTarget for endpoint binding
Doing so registers a shutdown task to workerprivate and prevents CC.
Differential Revision: https://phabricator.services.mozilla.com/D229822
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1932730
gecko-commit: df1c1dbfbe46bd3ec52697c8a128cf0f8f3ecadf
gecko-reviewers: asuth