www/squid: Update to 4.12 among other changes

• Update to 4.12
• Remove upstreamed patches
• Enhance rc script (thanks to Walter von Entferndt for ideas!):
  • create piddir if missing (/var/run may be a tmpfs)
  • don't wait endlessly if squid can't create a pidfile
  • define squid_group
• address GREASEd (thanks to Joshua Kinard and Juraj Lutter!)

PR: 247397
Submitted by: Juraj Lutter <juraj@lutter.sk>
Reworked by: maintainer
Approved by: maintainer
MFH: 2020Q3 (bug-fix release)
Sponsored by: Rubicon Communications, LLC (Netgate)