Allow gasLimit to be specified on eth_calls

[cag]

Related: #316

If trying to specify gasLimit on an eth_call, ethers.js will throw an Error: call cannot override gasLimit. Sometimes, being able to override the gas limit is desirable though, like when trying to determine how a different gas limit might affect the result of a call.

For example, eth_calling execTransaction on a Gnosis Safe with different gas limits to see where the transaction success value changes.

Also related: #299

Nodes will expect to see a gas parameter, and while eth_sendTransaction can be handled by signing transactions on the frontend, for eth_call to work, one would either have to allow/preserve the gas name expected by nodes or transform gasLimit to gas on the backend.

[ricmoo]

I was under the impression that call ignored the gasLimit, but I'll experiment and can add it as a valid call override.

[cag]

Something like this might be useful for checking:

contract EthCallGasDependent {
  function txGasEnough() external pure returns (bool) { return gasleft() > 20000; }
}

[ricmoo]

This should have happened as a consequence of the Contract refactor in 5.0.0-beta.189. Try it out and let me know if there are still issues.

[ricmoo]

This should be fixed now. If not, please re-open.

Thanks! :)