Character count can show incorrect count when going 'back', or if page is discarded and restored

[36degrees]

The character count can show the incorrect count when navigating back in the browser, or if the page is discarded and restored.

This is because the component is initialised before the form control state is restored, and is very similar to the issue described in #1794 and fixed in #1842.

Because of the similarity with those issues, I suspect this will affect Chromium browsers > 79 and Internet Explorer 8-11.