std/json does not support json5

[soyuta]

.luaurc is JSON5, but lute setup --with-luaurc fails whenever the file contains trailing commas or comments.

{
    "languageMode": "strict", 
}

> lute --version          
1.0.0

> lute setup --with-luaurc
Writing definitions at ~/.lute/typedefs/1.0.0
Successfully wrote type definition files to ~/.lute/typedefs/1.0.0
Writing luaurc file at path\to\.luaurc
@std/json.luau:231: JSON error - Trailing comma around 34
stacktrace:
[C] function error
@std/json.luau:231 function deserializerError
@std/json.luau:484 function deserializeObject
@std/json.luau:518
@std/json.luau:549 function deserialize
@cli/setup/init.luau:61

There is still no option like --with-config-luau, either, so it is difficult to include comments in the configuration.

However, this does not seem like a simple bug, since the issue occurs because @lute/json only parses standard JSON. Perhaps @lute/json should provide an option to parse JSONC as well.

Considering that not only .luaurc, but also Rojo’s .json files, use JSONC that is closer to JSON5, supporting only strict JSON may be limiting.
of course, if the goal is to keep the library small, it would also be reasonable for it to support only standard JSON

[astrorehan]

I opened #1302 with an opt-in JSONC mode: json.deserialize(src, { comments = true, trailingCommas = true }), defaulting to strict JSON so existing callers are unaffected.

I stopped short of full JSON5 on purpose. Unquoted keys, single-quoted strings, hex literals and Infinity/NaN would mean rewriting the value and string parsers, and comments plus trailing commas are the two things that actually block .luaurc and Rojo files. Glad to extend it if you would rather have the whole dialect.

One thing I left out: lute setup --with-luaurc can pass those options in a single line, but it then rewrites the file through json.serialize, which would drop any comments that were in it. That felt like a separate decision, maybe together with the --with-config-luau idea.