Add a page on the Output bottom panel

[Calinou]

While print_rich() works independently of RichTextLabel, it still makes use of BBCode. (I'm not sure if there is another location where this paragraph would be more suitable.)

[tetrapod00]

The written content looks generally good, but this is the wrong place to put it. Documentation for print_rich() does not belong on a page about RichTextLabel, even if they both happen to use BBCode.

The duplication of BBCode documentation is an ongoing problem, see #9998. Wherever this content ends up, you should probably link to the BBCode reference that already exists in this page. If the BBCode docs are ever consolidated, that link can be redirected to the new BBCode docs.

I am not sure what the best page to put this new content is. If we have a place that already documents print(), it makes sense, but I don't know if we do. Possibly a page in Scripting/Core Features/Debug is the right place (since prints can be used to debug).

[Calinou]

This PR now adds a new page on the Output bottom panel, which is linked to on the BBCode in RichTextLabel page.

[tetrapod00]

Looks good to me now, thanks for making extensive changes like this!

[mhilbrunner]

Thank you!