Discussion: mapbox controls

Nobody has claimed this yet.

Hi. I have [some controls](https://github.com/bravecow/mapbox-gl-controls) for personal usage.
What I like about them:
1. [each control have separate directory with js + css + icons](https://github.com/bravecow/mapbox-gl-controls/tree/master/src/ruler)
mapbox now have 600-lines CSS
2. valid CSS / SCSS, mapbox CSS is not: https://github.com/mapbox/mapbox-gl-js/blob/master/src/css/mapbox-gl.css#L154
3. injected icons inside control button: https://github.com/bravecow/mapbox-gl-controls/blob/master/src/ruler/ruler.js#L3:
* ~~no additional GET request for each resource~~
* ease of styling. we can style inline SVG with CSS.
* ease of resizing

As result:
* reduce JS bundle for mapbox
* removing `svg-load` plugin
* ~~remove some GET requests for icons~~
* remove CSS prefixes, use [autoprefixer](https://github.com/postcss/autoprefixer).
* move controls from this repo to reduce package.json deps (if any)
* controls will not use any internal events or methods. it will help to understand real needs and provide better API for users (e.g. no public event for style load #8765 for now)
* move mapbox language, mapbox draw and other controls to this monorepo. they will have same bundling tools, codestyle, docs, etc. I think it will make future support easier
* braking change

Start by reading src/css/mapbox-gl.css and comparing the linked mapbox-gl-controls src/ruler structure, including its JavaScript, CSS, and icons. Review the proposed package.json, bundling, and control API implications before attempting work; done would require a settled scope and migration plan for controls, dependencies, styling, and breaking changes.

Written by the indexing model from the issue text.