Fix filesystem edit_file literal dollar replacements

[kgarg2468]

Fixes #4157

Summary

• Treat edit_file replacement text literally when using the exact-match replacement path
• Use the callback form of String.prototype.replace so $, $&, $\``, and $'` are not interpreted as replacement patterns
• Add regression coverage for literal dollar replacement content

Tests

• cd src/filesystem && npx vitest run __tests__/lib.test.ts
• cd src/filesystem && npm run build
• git diff --check