Support martins' `/catalog`-api for font discovery

[CommanderStorm]

Created from:

• Support Fonts List martin#1610

Closely related to:

• Regression: Missing autocomplete/list of available fonts #945

Problem

Maputnik currenlly does request /font/%7Bfontstack%7D/%7Brange%7D to query for fonts if ran against maplibre/martin.
This is the case because the orinal font url is /font/{fontstack}/{range}.
As the .pbf ending that maputnik assumes does not exist, the replacement on line 30 below does not happen.

Related PR on martins side which we did not get done yet:

• Improved glyph url handling: accept arbitrary suffixes after {end} #1443 martin#1444

Maputnik expects to recieve an array of possible fontstacks.

Feature Request

would it be possible to request these 3 URLs in paralel and accept the first successfull response or would the overhead be too high on the maputnik side?:

• (idk which software this is) original URL
• (idk which software this is, its not tileserver-gl) /fontstack.json
• (tileserver-gl) replace(normPathPart, '.json')
• (martin) /catalog

Alternatives

We could handle this in martin. I am unsure what is the best option here.
A hybrid approach would be to drop the .pbf requirement in below code and implement serving under the replace(normPathPart, '.json')-Url in martin

Additional Context

maputnik/src/libs/metadata.ts

Lines 20 to 35 in c6174a5

	export function downloadGlyphsMetadata(urlTemplate: string, cb: (...args: any[]) => void) {
	if(!urlTemplate) return cb([])
	// Special handling because Tileserver GL serves the fontstacks metadata differently
	// https://github.com/klokantech/tileserver-gl/pull/104#issuecomment-274444087
	const urlObj = npmurl.parse(urlTemplate);
	const normPathPart = '/%7Bfontstack%7D/%7Brange%7D.pbf';
	if(urlObj.pathname === normPathPart) {
	urlObj.pathname = '/fontstacks.json';
	} else {
	urlObj.pathname = urlObj.pathname!.replace(normPathPart, '.json');
	}
	const url = npmurl.format(urlObj);
	loadJSON(url, [], cb)
	}

CC @nyurik @artyomb

Note

PS: I have a bit of time in my cristmas break to look into implementing this.
I think I am missing a bit of context as the code relevant seems a bit strange

[nyurik]

I would prefer to rely on the /catalog API, or possibly even query multiple endpoints - and see which one gives real result - and use that.