Provide event-specific event classes for use in WASM handlers

[Jannis]

WASM-only solution

There’s an easy solution that’s purely on the WASM side: We could generate

class AuctionCreatedEvent extends EthereumEvent {
  id(): Bytes { return this.params[0].value }
  assetId(): H256 { return this.params[1].value }
  seller(): string { return this.params[2].value }
}

When people then write handlers like

handleAuctionCreatedEvent(event: AuctionCreatedEvent) { ... }

they could use event.id(), event.seller(). (edited)
That requires no magic at all in Rust.

Rust solution

We could try using generics like

Event1<T>
Event2<T,U>
Event3<T,U,V>
...

and write Asc type conversions for the. The names of the parameters don't matter, just their order and their types.