Add freeze and preferNullPrototype options for parse() and .toJS()

[eemeli]

This adds freeze and preferNullPrototype options corresponding to the ones introduced by JSON.parse Options Proposal.

With freeze enabled, the Object and Array values corresponding to mappings and sequences are deeply frozen.

With preferNullPrototype, Object values corresponding to mappings are created with Object.create(null).

[fisker]

Why preferNullPrototype, not nullPrototype?

[eemeli]

Why preferNullPrototype, not nullPrototype?

Because that's the one currently in the upstream proposal: https://tc39.es/proposal-json-parseimmutable/#sec-createjsonparseoptions

Suggest you ask this question in its repo? https://github.com/tc39/proposal-json-parseimmutable

[fisker]

Strange, in README it's already nullPrototype https://github.com/tc39/proposal-json-parseimmutable/blob/1121274bdda960e8d777ede4e4190c539d549526/README.md?plain=1#L31