Call external editor to edit `executable-fold` and refresh

[hammerfunctor]

Is your feature request related to a problem? Please describe.

0001-1.-Add-alternate-force-eval-and-wrap-definition-of-a.patch.txt

Describe the solution you'd like

Call external editor to edit executable-fold and refresh. Useful for things like heavy tikz plotting.

Describe alternatives you've considered

Forget about existing excellent editors and improve the code editing experience in TeXmacs. Aesthetic but not worth developer's time.

Additional context

No response

[da-liii]

Aesthetic but not worth developer's time.

It's developers' joy!

[hammerfunctor]

It's developers' joy!

Of course, I mean, developers have things much more joyful than this to do.