Consider first-class support for Message Calls

[raulk]

Currently the Block->transactions field takes a TransactionFilter as an argument that can filter transactions with input data (i.e. messages). We can introduce first-class support for message calls, such that we allow retrieving the function signature and an array of parameters, only from those transactions that are indeed messages.

Just an idea:

block(number: 123) {
  messageCalls(matching: 'functionName(uint256,bytes32)') {
    param1: parameter(index: 0)
    param2: parameter(index: 1)
  }
}