Introduce TransactionReceipt and Log

[tilacog]

This PR introduces two new Ethereum types:

• TransactionReceipt
• Log

Since apiVersion 0.0.7, subgraphs can request transaction receipts inside event handlers, so, for now, TransactionReceipt is stored in Event.receipt (which is a nullable field).

This also bumps the npm version to 0.27.0

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This PR is a dependency of:

• Ethereum Transaction Receipts in Event Handlers graph-node#3373
• Allow event handlers to require transaction receipts graph-tooling#860

[neysofu]

Do you need another review? @tilacog

[tilacog]

Do you need another review? @tilacog

If it's Ok for you, it would be awesome! 😁

[evaporei]

I've commented on the graph-node PR about a couple of field names that might require change.

Also I think you need to add the Index variants here.

[tilacog]

Added a couple of PR's with the requested changes.