Add script to format and validate the style about osm-liberty

[pathmapper]

Thanks for your suggestion @kylebarron

In general I'm up for adding a package.json with @mapbox/mapbox-gl-style-spec as dev dependency to have gl-style-format available.

If we would use a Git pre-commit hook, than the style would only be formatted when doining a commit, right?

I think it would be useful to be able to format/validate the style any time while working on it.

What do you think about using a script instead which could be execute with e.g. npm run test to format/validate the style?

Later we could also add functionality to remove not needed default values which are bloating the style like "visibility": "visible" as this is a recurring request to remove them from PRs (see #61, #72 (comment), #71 (review)).

[kylebarron]

Correct, the style would only be formatted on commit.

I agree that format/validation at any time is good, however most of the time people will be making edits using Maputnik, which probably enforces a valid style, and with the online editor forces formatting correctly. I mostly see this as a workaround/second check while the Maputnik issue is being sorted out.

[pathmapper]

OK thanks, so let's implement this with a npm run ... script which could be executed at any time.

Yeah, this is a good workaround for people using Maputnik Desktop, but also generally useful (e.g. when modifying the style with a text editor).

Is this something you are interested to work on and submit a PR?

[pathmapper]

ref: #59 (comment)