native JSONC parsing

[aster-void]

Is your feature request related to a problem

nix can't natively parse JSONC.

more specifically, I had to manually remove trailing commas from bun.lock to parse it into nix object.

Proposed solution

add builtin function builtins.fromJSONC

JSONC doesn't have "one universal standard", but it's generally assumed to be JSON superset with C-style comments (// and /* */) and trailing commas allowed (but not required)

Alternative solutions

1. add support for JSON5, which is superset of JSONC and has a universal standard https://json5.org/
2. use some package from nixpkgs to parse it (IFD)
3. manually remove comments and trailing commas from JSONC to then parse with builtins.fromJSON

Additional context

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates

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