Investigate using more robust method for detecting updates to input fields in Dragon

[NickColley]

In the character count component we repond to user input and update the message below the textarea indicating how many words or characters they have left.

In Dragon updating the textarea we found did not trigger the usual events since Dragon edits the value of the field directly, so we currently are doing a polling loop checking for changes in the value feed.

This matches the approach in the accessible autocomplete, but there has been a suggestion for another approach which looks less hacky.

alphagov/accessible-autocomplete#164 (comment)

Only downside I can see is that it wont support IE8, which we would need to determine if that's an issue given that most users will be using Internet Explorer 11 with Dragon

See the original discussion here: https://github.com/alphagov/govuk-frontend/pull/959/files#r211678196

[NickColley]

I've done a bigger investigation here: #1530 (comment)

[NickColley]

Given my investigation I don't think there is a way to improve this while keeping IE8+ support, I'll close this for now but it can be reviewed for example if we adopt custom elements.