Adds dappId to combinator contracts

[acenolaza]

Closes #24

Changes

• Adds dappId immutable variable to all combinator contracts. These are set by reading the underlying proxy.dappId() (except for NormalizedApi3ReaderProxyV1)
• Casts underlying proxies to IApi3ReaderProxyV1
• NormalizedApi3ReaderProxyV1 now requires a dappId to be pass in the constructor
• Validates that proxies dappId are equal in ProductApi3ReaderProxyV1
• Replaces @api3/contracts imports with MockApi3ReaderProxyV1 test contract to make testing simpler

Notes

• The dappId immutable variable is needed because dappId() in IApi3ReaderProxyV1 is not marked as view
• The cast to IApi3ReaderProxyV1 still feels kind of wrong to me since the underlying proxies might be another combinator proxy which might not even expose a dapiName() function for example. I think it might be more accurate to create a IApi3ReaderProxyWithDappId or similar that inherints from IApi3ReaderProxyand adds a function dappId() external view returns (uint256);

[Siegrift]

@acenolaza I'll be able to review this only after my vacation, but I've assigned the other guys for the preliminary review.

[matejfalat]

I've checked the contract changes (didn't go over the tests) and IMO they're looking fine.

[matejos]

Changes LGTM, but I would also see your suggestion as a good thing to do.

I think it might be more accurate to create a IApi3ReaderProxyWithDappId or similar that inherints from IApi3ReaderProxyand adds a function dappId() external view returns (uint256);

[acenolaza]

Changes LGTM, but I would also see your suggestion as a good thing to do.

I think it might be more accurate to create a IApi3ReaderProxyWithDappId or similar that inherints from IApi3ReaderProxyand adds a function dappId() external view returns (uint256);

abb3cf3 this should improve the cast of the proxies to a valid minimal interface that adheres to only what is needed on these combinator contracts.

[Siegrift]

I'm thinking whether it could be simplified if we used the IApi3ReaderProxyV1 instead of the new interface, but I'm thinking if there was another reason why we didn't do it like that initially.

[Siegrift]

👍 LGTM