When extending a system: fixed, the first symbol for the fixed system should always be extended (copied from the counter being extended), since it is impossible to explicitly define a first symbol when the counter system is extends.
<rdar://problem/107320608>
Pull request: https://github.com/WebKit/WebKit/pull/12060
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/39251
Committed 262264@main (2eff4ba09737): <https://commits.webkit.org/262264@main> Reviewed commits have been landed. Closing PR #12060 and removing active labels.