Extract infos from from define.ml and meta.ml into JSON files

[Gama11]

@Simn and I talked about how it might be a good idea to extract the desscriptions / "used on" info etc of defines into a JSON file. That seems more natural for something that's essentially just data than a source file.

If it's done for define.ml, it only makes sense to do the same for meta.ml. Technically we even have a JSON structure defined already for metadata due to the display API.

This would have the nice side-effect that other tools could parse it and do something with it, for instance auto-generating some Haxe Manual pages that always seem to be slightly outdated ^{[1] [2]}. @markknol said he added some additional infos to some of those things, perhaps the JSON could have "extended descriptions" in a separate field, or use markdown in the description that is post-processed away for the command line output.

[kLabz]

Yeah!

I planned to do something similar, although only for meta.ml: generate HaxeMeta.hx, an @:enum abstract to String to be used in macros. Maybe such an abstract could be included in haxe std (in haxe.macro maybe?).

[Gama11]

That does seem like an interesting idea! I currently also maintain a (very incomplete) list of constants for metas in the language server because I wanted to avoid repeating string literals everywhere.

[kLabz]

Yeah, plus it avoids typos and provides some documentation on autocomplete.