feat: use extcodesize for isContract to reduce gas

[julianmrodri]

#2310

Fixes #2310

• Restablishes extcodesize to check if an address isContract as this now consumes less gas than extcodehash.

[julianmrodri]

@nventuro @frangio just implemented the change so we have it there. I will run some verifications to confirm less gas is consumed with this method.

[julianmrodri]

Execution costs (tested on Remix - solidity 0.6.6):
extcodehash

1. If address is EOA: 1079 gas
2. If address is contract: 1099 gas

With extcodesize:

1. if address is EOA: 1015 gas
2. if address is contract: 1015 gas

So there is a reduction in the execution costs by using extcodesize. Whether it iss significant I will leave it up to you guys, would really appreciate to understand your rationale.

[frangio]

Thanks @julianmrodri! I wouldn't call the reduction significant but it's still a welcome change!

Can you add a small changelog entry?

[julianmrodri]

Sure will do right now.

[frangio]

Thanks!