• Update the 12.0 schedule to reflect releng/12.0 has branched, and 12.0-RC1 builds have started.
• Add stable/12 and releng/12.0 to the security page.
• Add releng/12.0 to the releng index page.
• Document __FreeBSD_version 1200500.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation