Be prepared for 32-byte addresses

### What is wrong?

https://ethereum-magicians.org/t/increasing-address-size-from-20-to-32-bytes/5485

At some point the protocol is likely to expand addresses to 32-bytes. There may be assumptions that are being made about addresses that could at minimum be aware that this change is coming.

### How can it be fixed

:shrug:

Just be ready for this.... in whatever way is appropriate.

The issue names no files, tests, or entry points. Start by reading the linked Ethereum Magicians discussion, then search the compiler for assumptions about 20-byte addresses. The issue provides no concrete completion criteria, so scope and a definition of done need to be agreed before implementation.

Written by the indexing model from the issue text.