Add the required sys call MSC_iokit_user_client_trap to the WebContent process' sandbox on macOS.
Pull request: https://github.com/WebKit/WebKit/pull/800
<rdar://93600722>
Committed r294511 (250768@main): <https://commits.webkit.org/250768@main> Reviewed commits have been landed. Closing PR #800 and removing active labels.
Re-opened since this is blocked by bug 240697