Anonymous procedures defined outside of the main code tab give unhelpful code locations

[LaCuneta]

I discovered this while working on #2239. If you add a global to a model and set its value to an anonymous procedure inside a button, then a runtime error occurring in that procedure gives unhelpful information about where it occured:

• If it's a command it gives a small stack trace in the error window, but that trace doesn't indicate the code lives in a button.
• If it's a reporter it gives the same short error message, but jumps to the code tab and highlights the incorrect code, likely the offsets from where the reporter definition lives in the button.

I did not test other possible source locations, such as includes files or (shudder) plot commands.

Related is #427, which I think would make implementing and testing this much simpler and should be prioritized over these limited edge cases.