Consolidate input aria documentation and tests

[andysellick]

This PR has been updated and no longer does what it originally did.

What

Consolidate the aria attribute documentation for the input component.

A possible future change (for more than just this component) could be to pass any required aria attributes to components rather than having to add new options for each new use case, as below.

<%= render "govuk_publishing_components/components/input", {
  label: {
    text: "This is an example only and may not work with a screen reader"
  },
  name: "labelledby",
  aria: {
    describedby: "wrapper",
    controls: "wrapper"
  }
} %>

aria ||= []
<%= tag.input name: name,
    aria: aria
%>

Visual Changes

No visual changes.

View Changes

https://govuk-publishing-compo-pr-1062.herokuapp.com/component-guide/input

[NickColley]

Could we avoid doing this by updating the pattern on that page to match the current recommendations for errors? I don't believe we promote using aria-invalid at the moment, so might be able to simplify things this way.

[NickColley]

I've made an example of this: https://govuk-frontend-local-council.glitch.me/

[NickColley]

@36degrees did an investigation here: alphagov/govuk-frontend#1168

[andysellick]

@NickColley you're absolutely right. I was so busy trying to implement this feature I didn't stop to consider if we actually needed it or not. I've reworked this PR to not have this addition but still have the consolidation of the aria examples and tests, which I think is worth keeping. Thanks!