Mapbox-gl-js: Move mapboxgl.supported logic into standalone module

[lucaswoj]

Presently, end users are required to include all of mapbox-gl.js in order to test if it is supported. This is impractical for bandwidth-conscious users who are implementing fallback to mapbox.js.

[c0]

:+1:

This would greatly improve the experience for Android devices that don't support WebGL. We could use this to _only_ download the GL or raster code and not double up. Critical for 2G/3G networks.

[mmperryman]

Agreed, I'd love to see a solution for this.

[lucaswoj]

I have moved the necessary logic to https://github.com/mapbox/mapbox-gl-js-supported

Next Steps

• [x] have another engineer review https://github.com/mapbox/mapbox-gl-js-supported
• [x] publish the new module to npm
• [x] use the new module within Mapbox GL JS
• [x] move any relevant issues from this repo to the new repo

[lucaswoj]

@bhousel Does this look ready to 🚢?