`contenteditable="true"` wrapper needs tabindex for accessibility

[ewan-spence]

I am working on a form, and have had to create my own "simulation" of a tab key press (i.e, cycle to the next input/clickable node in the DOM). In implementing this, I have discovered that there is no way of tabbing into the SunEditor component in a way that the user can immediately start typing.
I know that my problem can be solved simply by adding tabindex="0" to the "se-wrapper-inner" div that contains the HTML being entered, as I did so myself with DevTools and my "manual tab", as it were, worked as expected. I believe this would be a simple change, but may have unintended consequences