Avoid calling os_log_copy_message_string on secondary thread, since it is not a performance bottleneck.
<rdar://problem/109723241>
Pull request: https://github.com/WebKit/WebKit/pull/14251
Committed 264584@main (3022cdc9fa3b): <https://commits.webkit.org/264584@main> Reviewed commits have been landed. Closing PR #14251 and removing active labels.