`project.json` and `manifest.json` are `jsonc` and cannot be parsed by `std::encoding::json`

[Ecoral360]

It is quite awkward that we cannot use the std::encoding::json parser to read the standard project.json or manifest.json.

Proposals :

1. Make project.json and manifest.json valid json by removing comments and trailing commas.
   OR
2. Renaming project.json and manifest.json to project.jsonc and manifest.jsonc to better communicate the different format and avoid misleading users.
   + Add a jsonc compatible parser in the standard lib.

[BWindey]

I would propose to update std::encoding::json::parse to take in an optional parameter strict = false that will allow trailing commas.

Additionally add a jsonc parser. Not sure how much code you could reuse from normal json parser, but looking at the code it seems pretty doable.