Migrating all Immutable X contracts and tests

[alex-connolly]

Aims to merge all the contracts used by Immutable X customers into our central contracts repository. Contracts sourced from:

• https://github.com/immutable/imx-contracts
• https://github.com/immutable/ts-immutable-sdk/tree/main/packages/internal/contracts

[rzmahmood]

• Does it make sense for the version of these contracts to stay at ^0.8.x?

• Does it make sense for us to bump the contract versions to 0.9.x when that comes out? I don't see that happening for contract like Registration.sol as it doesn't make sense to update the version of a deployed contract, causing a mismatch. This will eventually cause commands like npx hardhat compile to fail once other contracts start being written in 0.9.x. Consider what the development strategy will be then.

[carleeto]

• Does it make sense for the version of these contracts to stay at ^0.8.x?

Yeah, I think it does for now.

• Does it make sense for us to bump the contract versions to 0.9.x when that comes out? I don't see that happening for contract like Registration.sol as it doesn't make sense to update the version of a deployed contract, causing a mismatch. This will eventually cause commands like npx hardhat compile to fail once other contracts start being written in 0.9.x. Consider what the development strategy will be then.

Probably not. If contracts use multiple versions, we can use a hardhat config to deal with it (https://hardhat.org/hardhat-runner/docs/advanced/multiple-solidity-versions)