V8: Support auto focus on ACE editor and use it for RTE source view

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes #5363

Description

See excellent steps to reproduce in #5363.

This PR introduces an option to auto focus the ACE editor, and said option is then used for the RTE source view. When applied it works like this:

[emmaburstow]

Hey @kjac

Excellent giffing! Thanks for the work. Speak soon,

Emma

[christophnz]

Nice, thanks for fixing! Hope this makes it into the next release soon.

[nul800sebastiaan]

Thanks @kjac ! I haven't looked at this yet, but how hard would it be to get rid of the horizontal scroll bar as well here?
There's a separate issue for that here: #5220

But I'd be happy if that can be fixed in this PR too, no need for a separate one.

[kjac]

@nul800sebastiaan I did dig into it, but it's not so easily fixed. The horizontal scroll bar shows up because of some inline styling and explicit widths applied by the ACE editor; maybe due to some outer element absolute positioning, maybe due to something else I can't see at the moment. In any case I believe the scrollbar issue should be solved on its own.

[nul800sebastiaan]

Okidoki, thanks!

[kjac]

...well I'll be damned. Seems there's an ACE option that can be set after all!

I'll update this PR 👍

[kjac]

...and now the lines wrap nicely:

[nul800sebastiaan]

This is great, thanks very much! 👍