Add support for TransactionExtension

[pgherveou]

PR #3685 introduced a new TransactionExtension trait. These new extensions should be more flexible than its predecessor SignedExtension and should let us write custom logic to define custom origin authorization.

This should be used to authorize Ethereum transactions, instead of the current pipeline that wraps the UncheckedExtrinsic trait and introduces a custom Checkable implementation. This change will result in a fairer weights to extract the signer and decode the ethereum transaction, and should make the integration of the ethereum compatibility layer less invasive and easier to integrate in the runtime.

See https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/examples/authorization-tx-extension

[pgherveou]

@athei is that something we still want to do, you got more insight than me about this with your recent work on gas mapping

[athei]

Yes. But it will be a huge effort we will tackle once the current system runs stable and we setup all the regression tests.

[0xOmarA]

Is this something that still needs to be done? I can see that the revive codebase has no more SignedExtension references and that EthExtra::ExtensionV0 requires an implementation of TransactionExtension