add support for multiple elements

I extracted https://github.com/kellyselden/ember-text-test-helper from an app without knowing hasText does whitespace collapsing. I would like to ditch my addon, but to reach feature parity, this project would need to support selectors that match multiple elements and “combine”, as well as assert.dom(document.querySelectorAll('div')).

I think @Turbo87 is open to it, but every assertion will need to be updated. For instance hasAttribute will probably turn into a “all have attribute”.

[runspired]

@Turbo87 how about either:

assert.dom("selector")
  .exists({ count: 2 })
  .at(0) // get the first index and continue chaining from there
  .hasAttr("thing");
  
assert.dom("selector")
  .exists({ count: 2 })
  .each((dom, index) => {
     dom.hasAttr("thing"); // continue asserting with each of the individual things
  })

[runspired]

@Turbo87 to be clear I’m not proposing accessors, though that would be a powerful eject button I wouldn’t mind having, I’m proposing the ability for it to return new instances of assert.dom on an individual item of the list found by original selector. This would massively cleanup a lot of dom assertions I’ve seen, and also naturally be bounded to a single level of decomposition since it’s not possible to further select within a selected element ❤️