Require "--" as an argument terminator when running noninteractively

Summary:
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.

Test Plan: Ran various commands. Welded non-UTF8 files.

Maniphest Tasks: T13490

Differential Revision: https://secure.phabricator.com/D21002