Further cgx debugging improvements

[Korijn]

I just wanted to put it out there that it is technically possible to also make the <template> section (or the render function really, depending on how you look at it) debuggable.

You would need to ensure the generated render AST is not one big return statement, but instead has separate lines corresponding to the individual elements in <template>, and then maintain a lineno mapping while generating the AST statements.

This is how Vue does it, too!

I wouldn't recommend diving into this right away but just wanted to make you aware of the possibility.