doc: refactor manpage to use mdoc(7) macros

NOTE: A correctly-written commit message will be amended and force-pushed once a maintainer gives their approval. Due to the rather ambitious nature of this PR, and the fact it targets an ancillary part of Node's codebase, I expect this to be rejected. I thought to try nonetheless.

Checklist

• documentation is changed or added
• commit message follows commit guidelines

Description

This is a refactoring of Node's manpage to use mdoc macros instead of the legacy man macros. Both are widely supported, and both are used to format manual-pages for terminal display. The key difference is that mdoc is semantic rather than presentational. It offers less control over arbitrary formatting, but generates very consistent output. Its syntax is a little unwieldy but leaves less room for error. See mdoc(7) for reference.

Realistic preview of changes

• Before (using man macros)
• After (using mdoc macros)

Some minor editorial changes were made so the page conforms to the structure and conventions of manpages. In addition, the --experimental-modules and --experimental-vm-modules switches were added to the OPTIONS section, which are currently listed in the output of node --help.