Add collections access API for shortcodes

[cmcknight]

Is your feature request related to a problem? Please describe.
I am trying to access a collection from a shortcode. While I can pass in the collection currently used by the template as an argument to the shortcode, I am unable to access other collections from within the shortcode.

Describe the solution you'd like
Ideally I would be able to use the following syntax:

eleventyConfig.addShortcode('getMfr', mfrId => {
  let mfr = collections.getItem('collection name', item => item.mfrId === mfrId)
  return mfr
})

Describe alternatives you've considered
My current workaround is to use the following:

  eleventyConfig.addShortcode("getMfr", mfrId => {
    let mfrData = JSON.parse(fs.readFileSync('./src/_data/manufacturers.json'))
    let mfr = mfrData.find(obj => obj.mfrId === mfrId)
    let text = `<a href="${mfr.url}" target="_blank">${mfr.name}</a>`
    return text;
  })

I've also tried:

const mfrData = require('./src/_data/manufacturers.json')

Both work, but they feel inelegant...

Additional context
My goal is to avoid the need for a backend database until it's really necessary. For building a static site, if it's not an Amazon.com, it's likely that it's unnecessary.

[pdehaan]

Related #813, but based on the comments, I think you found that already.

[cmcknight]

Related #813, but based on the comments, I think you found that already.

Yes, I had reviewed that earlier and posted my workarounds there as well. :-)