Add `--fix-dry-run` option

[jopemachine]

Fixes #663.

Eslint doesn't expose fixDryRun option in programmatic API. fixDryRun is internally translated to fix option and don't call ESLint.outputFixes. (Ref: https://github.com/eslint/eslint/discussions/15877)

So I think xo could handle this option similarly. fixDryRun is translated to fix option before passing to ESLint constructor, and xo.outputFixes would not be called since the fix option is false.