Syntax Highlighting for "JSON with Comments" a.k.a. jsonc

[harmathy]

Problem

In JSON there are no comments allowed. This is also honored by Github syntax
highlighting in fenced code blocks:

{
    // Note: there might be additional sizes available
    "sizes": [ "S", "M", "L", "XL", "XXL" ]
}

There is also "JSON with Comments" or jsonc (see Github language list)
which allows C-style comments

{
    // Note: there might be additional sizes available
    "sizes": [ "S", "M", "L", "XL", "XXL" ]
}

This is prominently used in tsconfig.json, jsconfig.json and
vscode configuration files.

It would be nice to have syntax highlighting support for such code blocks.

A code fence with jsonc should be highlighted:

```jsonc
{
    // Note: there might be additional sizes available
    "sizes": [ "S", "M", "L", "XL", "XXL" ]
}
```

Proposed Solution

• Support for "JSON with Comments" in highlight.js: Add a JSONC language variant for "JSON with Comments" highlightjs/highlight.js#2016
  • this adds rendering of C-style comments to normal JSON
• jsonc alias also available: Add "jsonc" alias highlightjs/highlight.js#4018
  • seemingly not yet contained in a stable release

Notes

If #2313 is considered, Prism seems to render also render comments in normal JSON, but there is no jsonc alias.

[ehuss]

As a workaround, I'd recommend using the javascript language tag.