enhanceSelectElement does not correctly link to existing hint or error message

[edwardhorsford]

When using the enhanceSelectElement, an autocomplete may have a hint or error message, but unfortunately these are not linked with aria-describedBy from the input - so assistive technologies cannot get them.

The fix for this would be for the autocomplete code to grab the existing ids from aria-describedby from the select it's enhancing, and include those in addition to the instructions span it adds.

In the mean time, a fix is that the instructions added by the autocomplete are configurable by teams. We can make sure the instructions include any existing hint / error message.

When initialising an a given select as an autocomplete:

• Get the ids mentioned in the select aria-describedby - there can be more than one when the field is in error.
• Get the text content of those elements.
• Concat the text content together.
• Append with any instructions for AT for how to use the autocomplete
• provide this as tAssistiveHint when initialising the autocomplete.

[edwardhorsford]

An alternate solution would be to use js to look up the original contents of aria-describedBy in the original select, then prepend these to the generated input.