Defines types for the extended metadata of ink! smart contracts targeting [`pallet-revive`](https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/revive/) of
[Polkadot SDK](https://github.com/paritytech/polkadot-sdk).
Currently part of [`cargo-contract`](https://github.com/use-ink/cargo-contract), the build tool for smart
contracts written in [ink!](https://github.com/use-ink/ink).