Generate fixtures.json files for components on build:package

[vanitabarrett]

Resolves #1895

What

Adds steps to the build:package task to generate fixtures.json files for each component in the following format:

{
  "component": "button",
  "examples": [
      {
        "name": "default-example",
        "options": {
           "text": "Save and continue"
         },
         "html": "<button class=\"govuk-button\" data-module=\"govuk-button\">\n  Save and continue\n</button>"
      }
   ]
}

Fixtures files contain the component name and all examples with the output html to allow maintainers to test their own HTML against ours

[36degrees]

This is looking really good – great to have tests that cover this as well.

[36degrees]

It's a bit strange to write the file out from the task, rather than passing it out and letting gulp handle it. It's definitely strange that we write the two files in two different ways.

I think there's probably a more 'gulp-like' way of doing this, but my gulp knowledge is lacking…

If not, and we stick with using fs.writeFileSync here I think we should write both files from within the task?

[36degrees]

Separately, we use 4 space indentation for params.json, so we should probably be consistent and use the same here.

[hannalaakso]

This looks really good to me 👍 Agree with @36degrees that it would be good to generate the two files in a similar manner.

[vanitabarrett]

@hannalaakso @36degrees Thanks both - I think I've addressed those comments now. I've also added a second commit to create separate functions for the fixtures and macro-options gulp tasks - I think it makes it a bit easier to quickly scan the gulp task and see what's happening, but happy to leave that change out if people don't find it helpful!

[36degrees]

Looks good to me, with a couple of minor comments 👍🏻

I think it might be revisiting this task some point soon as it feels like it's becoming a bit of a 'monolith' task with too many responsibilities – the two JSON-generating functions could be separate dependent tasks?

That would also make it possible to update just the JSON files without having to run all of the other changes, which feels like it might be useful.

[hannalaakso]

Nice work 👍

[vanitabarrett]

Needs rebasing against master once #1924 has been merged