Draft: Fix #10307 scheme display effective

Draft. Needs work in the code and in the document.

See the document in the MR in /plug-ins/script-fu/docs/messaging-and-errors.md

It does show how the issue could be fixed. It is working, but someone else needs to review whether the solution is good, and certain scheme functions should be variadic, and the style is not standard.

Milestone 3.0.2. Issues for 3.0 are more pressing. Seems like a lot of trouble just to get (display ...) writing to the terminal.