Recursively freeze JSON bindings/modules

[isker]

workerd should recursivelyFreeze JSON data parsed directly from its config. In my mind, these values are application-wide configuration, the mutation of which when handling a request has the potential to result in subtle but serious bugs. It may not be obvious to developers in shared codebases that an object/array they're dealing with is ultimately a perhaps deeply-nested property of a global mutable object. I have unfortunately seen it happen before 🌞.

But of course this would be a breaking change.