Is your feature request related to a problem? Please describe.
This issue is a bit of a nit. We have this folder called standards that currently just contains some Uniswap contracts: https://github.com/ethereum-optimism/optimism/tree/master/packages/contracts/contracts/optimistic-ethereum/libraries/standards. I don't quite think this is the right place for these contracts. Perhaps we could consider adding a folder contracts/external/uniswap instead?

Describe the solution you'd like
I think contracts/external/uniswap makes sense. Ideally we would separate out the contracts that we've written from the external contracts we're using.