[Color system] Add color factory and build modern tokens

[danrosenthal]

Merging the next branch into master, which includes several changes after the v2.7.0 release, as well as the latest changes incorporating the color factory into tokens, and using TypeScript in the build for modern tokens.

Release candidate on UNPKG: https://unpkg.com/browse/@shopify/polaris-tokens@2.8.0-rc.0/dist-modern/

This will all be released as v2.8.0, since these changes are not breaking.

[danrosenthal]

@kaelig, should we be merging f471512 and 68772b3 into master along with this, or should those remain unmerged in the next branch?

Looks like those should not be merged to master. I will drop those commits from this PR.

[BPScott]

RC package contents look good to me from looking at unpkg, though I haven't tried using it within polaris-react to confirm end-to-end

[kaelig]

I thought the convention was single quotes – if so, can you check if there is a Sass or Prettier configuration issue?

[danrosenthal]

@BPScott updated the prettier config to not format these files, so not an issue.

Ben, what was your rationale there?

[BPScott]

This was deliberately changed - The docs folder is no longer formatted with prettier (but I do use sass's expanded style to maintain most of the readable formatting :)

I split the build into "legacy", "modern" and "docs" steps, this makes it easy to do just the modern build in shipit (to generate the dist-modern folder), and also change the docs build to something new (probably a proper gatsby app) in the near future. In order to retain the old behaviour I would have had to either:

• have two steps "build-legacy:format" (to format the dist folder with prettier) and "docs:format" (to format the css in the docs folder with prettier) to that run after each of the build-legacy and docs steps
• A single step that runs after both "build-legacy" and "docs" - which makes makes the of steps a bit more convoluted and less self-contained.

I figured seeing as this file is generated content, and is going away imminently it is easier to only create a build-legacy:format step that formats just the dist folder, and skip formatting the docs folder css with prettier, as sass already does a pretty solid job. Incidentally I've just realised by formatting this file after sass does its thing we risk breaking the css.map file that the sass build generates (as that maps locations in the not-prettiered css file, not the version that's been ran through prettier)