Link code fragments to core/asm output

[tomsmeding]

The Godbolt compiler explorer has this for asm. The idea is to let the playground UI indicate, in some fashion, which parts of the Core or assembly dump corresponds to which part of the source code. I'm not sure how exactly this should work for Core, but for assembly the relevant information is apparently present in info tables (suggestion due to Gergő Érdi).

This would be a sizeable change, adding significant amounts of code to both the worker and the web interface.