Allow to override the EVM version per language when compiling

[danhper]

What I did

Allow to override the evm_version per language, e.g.

compiler:
  evm_version: london
  solc:
    version: 0.8.9
  vyper:
    evm_version: istanbul

How I did it

compile_and_format can now either take a string or a dict that must map all the used languages (Vyper and Solidity) to their desired EVM version.
The change is fully backward-compatible.

How to verify it

Try the YAML config given above.

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

[joshim2021]

427131bbac