Use a null prototype to represent YAML maps

[remcohaszing]

Is your feature request related to a problem? Please describe.
YAML defines maps. YAML maps map really well to the JavaScript Map type, but this is often inconvenient to use in practice. So I think the current default to use a plain object by default makes sense.

The problem however, is that the default Object prototype has some default properties. This may lead to bugs, such as prototype pollution. While I don’t expect to see this happen inside of this package, it might happen in user code that consumes the values used with this package.

Describe the solution you'd like
Use the null prototype for parsed YAML maps.

Describe alternatives you've considered
N/A

Additional context

• https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object#null-prototype_objects
• https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/Prototype_pollution#create_javascript_objects_with_null_prototype
• This is also used in other places where a plain object represents a map, such as RegExp capturing groups.

[eemeli]

This makes sense, but definitely only as a part of the v3 update, as this would be a breaking change. If you're interested in working on this, I'd be happy to review a PR?