fix: only update type snapshots if process.argv includes --fix

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes Running eslint without --fix still updates snapshots #14
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Only adds a fix() function if process.argv.includes("--fix"). This will therefore stop type snapshots from being updated automatically when ESLint is run through the Node API, such as in an editor extension.

This is the best I can do without ESLint providing a native way for rules to know whether they're in fix mode 😬. I don't like it. It's a rough heuristic and I'll file a followup issue on improving it (that will be blocked on ESLint's making an API, I assume).

This also isn't tested yet so I'll file a followup issue for that too.

[codecov]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (7ffdbab) 83.15% compared to head (4dcb4cb) 81.83%.

Files	Patch %	Lines
src/rules/expect.ts	51.85%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
- Coverage   83.15%   81.83%   -1.32%     
==========================================
  Files          10       10              
  Lines         843      837       -6     
  Branches       94       93       -1     
==========================================
- Hits          701      685      -16     
- Misses        142      152      +10     

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