Move WebCodecs VideoFrame serialisation out of agent cluster tests to a separate file
<rdar://problem/114750260>
Pull request: https://github.com/WebKit/WebKit/pull/17280
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/41729
Committed 267545@main (ab6979eff99f): <https://commits.webkit.org/267545@main> Reviewed commits have been landed. Closing PR #17280 and removing active labels.