Enable fetch priority hints by default
<rdar://problem/107630350>
Pull request: https://github.com/WebKit/WebKit/pull/12393
Committed 262623@main (48bfdb0c9053): <https://commits.webkit.org/262623@main> Reviewed commits have been landed. Closing PR #12393 and removing active labels.
Re-opened since this is blocked by bug 255062
Pull request: https://github.com/WebKit/WebKit/pull/16939
<rdar://106852027>
Committed 267196@main (793f132ba08b): <https://commits.webkit.org/267196@main> Reviewed commits have been landed. Closing PR #16939 and removing active labels.