Polkadot: Reverts return encoded error data

[xermicus]

This is a continuation of #1415. require(), assert() and revert() now return error data, according to the Ethereum Solidity documentation. Additionally, many reverts inserted by the compiler now return the corresponding Panic(uint256) error data, to align Solang closer with solc.

The error types known to the contract are added in the metadata lang_error field. At the moment there are only Error and Panic because we don't support custom errors yet.

Refactored revert-related code into a dedicated codegen module to. Refactored the polkadot::errors into distinct tests, made them less brittle and added assertions for the execution output.

I'm now working on a follow-up PR for bubbling up uncaught exceptions (this is why it's already included that in the documentation).

[seanyoung]

Great stuff just some minor things

[seanyoung]

There are still comments open when you requested a review from me

[seanyoung]

Please

[seanyoung]

So where does the name go? E.g. Panic, Error, or CustomError5?

I do think this this paragraph is inscrutable. I still don't have a good idea of what is going on here.

[xermicus]

Makes me think, do you think it'd be better if the Selector bytes goes into the path of the Variant Type?

[xermicus]

I've rewritten it and added an example.

I also removed that the selector can be reconstructed. We don't guarantee this for messages selectors, so I doubt whether we can guarantee this for errors once we introduce custom errors. And including the selector directly is better anyways and makes this unnecessary anyways.