This was renamed in 2018 (https://github.com/w3c/ServiceWorker/pull/1333) but no bug was filed with WebKit, sorry about that. Anyway, this is that bug. I don't expect the rename to cause problems in the wild.
Test to fail if targetClientId is present https://github.com/web-platform-tests/wpt/pull/29213.
As part of sorting out many errors in the browser compat data for FetchEvent in https://github.com/mdn/browser-compat-data/pull/10774, I noticed that no browser has shipped replacesClientId yet.
WebKit exposes targetClientId so I guess we should do the migration to replacesClientId even if no other browser supports it. We can deal with this as part of bug 190313
targetClientId was removed in bug 235107, but replacesClientId wasn't implemented.