Depends on D21001. Ref T13490.

• Require "--" to terminate arguments when running noninteractively.
• Don't correct spelling when running noninteractively (we still suggest corrections).
• Remove old "phage" wrapper script.
• Fix an issue where "argv" could implicitly generate a parseable "--argv" flag.
• Accept "--" as an argument terminator even when there is no argument list.
• Update some strings to use more modern quoting style.
• Make workflows decline to handle signals by default.
• Allow "arc weld" to weld non-UTF8 files together.

Ran various commands. Welded non-UTF8 files.