[mlir][ODS] Add support for specifying the successors of an operation.

This revision add support in ODS for specifying the successors of an operation. Successors are specified via the `successors` list:
```
let successors = (successor AnySuccessor:$target, AnySuccessor:$otherTarget);
```

Differential Revision: https://reviews.llvm.org/D74783