Include encoded return data in transaction trace

[sparrowDom]

What I did

The transaction trace didn't include the encoded return value of function calls if there was no source code contact information. This PR always includes the return data (when not null). If contract source code information is available, the returndata gets overridden by return_value.

Related issue: #1360

How I did it

I've decoded the returndata in the loop that loops through the trace steps before it chooses to ignore a step that doesn't have contract source code information available.

How to verify it

Run call_trace(True) on any transaction. Example before:

Example after (including this change):

Checklist

• I have confirmed that my PR passes all linting checks
• I have included test cases
• I have updated the documentation
• I have added an entry to the changelog

[iamdefinitelyahuman]

Cool!