chore: Change JSON::compute_keyhash_and_sort_json_entries to have pub(crate) visibility

[aakoshh]

Description

Problem*

This should allow noir-lang/noir#10736 to be merged

Summary*

Changes the visibility of JSON::compute_keyhash_and_sort_json_entries from private to pub(crate), to allow it to be called from JSON::parse_json with the changes noir-lang/noir#10736 introduces.

Additional Context

The compute_keyhash_and_sort_json_entries is defined in the keymap module, while the JSON structure and the parse_json method are in the json module. The keymap and json modules are siblings, so they shouldn't see each others' privates. There was a loophole for impl blocks, where they acted as if we were in the same type, regardless of the surrounding module, but this is not correct (or at least not how Rust works; it makes it harder for modules to isolate their functionality from each other).

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.