Debugger won't decode return values from non-Solidity transactions

[haltman-at]

Issue

The debugger will decode the return value at the end of a transaction, but it doesn't support this for Vyper. Because return value decoding is ABI-based and Vyper uses the same ABI as Solidity, doing this shouldn't be too hard; it just isn't possible at the moment due to some awkwardness with the debugger internals. Still, it shouldn't be too hard and it's something we should do.

[haltman-at]

Note: This problem will also apply to Yul once we support Yul (#1906). (Yul has no ABI, of course, but the problem still applies to return values from constructors.) Again, this is purely a problem with debugger internals. More specifically the issue is that it relies on there being a ContractDefinition AST node for the contract. This shouldn't be necessary; it's just arranged that way at present. So the problem is to rearrange it so that's no longer a requirement for decoding.