hardhat support

[zomglings]

Currently, running a hardhat compile in a repo that contains @moonstream/contracts imports breaks.

This is because there is no @moonstream/contracts package on NPM and hardhat uses NPM packages to manage dependencies.

See conversation on Moonstream Discord: https://discord.com/channels/867156607644860418/954495097406382120/1015381496082726983

Thanks to defikris for pointing this out.

This is what we need to do to enable hardhat support:

• Add package.json in contracts/ directory. We can base it off of the Open Zeppelin one: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/package.json
• Replace all @openzeppelin-contracts imports with @openzeppelin/contracts imports in Solidity files (thanks to @Yhtiyar for pointing this out)
• Update brownie-config.yml to reflect the new remapping for Open Zeppelin imports

[Yhtiyar]

Foundry is using hardhat-preprocessor to deal with remappings:
https://book.getfoundry.sh/config/hardhat