Make xdebug breakpoints work in all code files

[jegelstaff]

Right now, our code blocks are often included into other code and then executed separately in different files. It would be better if they were included natively, and then we could set debug breakpoints in them directly.

This is complicated in the case of derived value formulas, and possibly others, in part because we modify the code before execution. If derived values use the regular $elementName syntax then this would become easier.

[jegelstaff]

See also #574