- Shallow-freezing of objects is never used in our codebase, so remove
that code path.
- Deep-freeze is bugged in recent versions of SpiderMonkey (see bug
https://bugzilla.mozilla.org/show_bug.cgi?id=1930258). Until a fix
and/or a better API is provided, reimplement this feature by
recusively freezing object properties.
- Add tests for the deepfreeze function.