Helper methods for decoding log parameters on generated graph-ts types

[itsjerryokolo]

A user on discord brought this up,. They wrote
"It really feels like there should be a Log.decodeParameters(EventType/signature) helper that responds with Array based on the generated abi codegen types"

This will be particularly helpful in the handlers when using transactions receipts.
cc @incrypto32 @saihaj

https://thegraph.com/docs/en/developing/graph-ts/api/#events-and-blocktransaction-data