Better error output

[der-stefan]

When working on the JSON file, you sometimes make small mistakes like forgetting a comma, trying out comments (which don't work). All that tilemaker says is
Invalid JSON file.

It would be helpful if there is a better error message that actually helps in debugging the style file.

[etienneJr]

trying out comments (which don't work)

tip: this is how I add comments in the json file
https://codeberg.org/cartes/serveur/src/commit/fc3bbff08bd2dbb6f886020984ca553f2679ae32/tilemaker/resources/config-openmaptiles.json#L16