Milestone 3. Events with indexed fields are not encoded correctly

[xermicus]

If an event has fields declared indexed, they should be passed into the Substrate topics. This is not implemented correctly today. Ensure that indexed fields are passed into topics and add an integration test for this at

https://github.com/hyperledger-labs/solang/tree/main/integration/substrate

Success means that a pull request has had all its review comments addressed and it is merged.