swift

f075e4eb - Change DiagnosticBehavior into a struct enum so we can put methods on it.

Change DiagnosticBehavior into a struct enum so we can put methods on it. The reason why I am making this change is because I want to put a merge operation on DiagnosticBehavior. This merge operation allows for DiagnosticBehavior to work like a lattice. When one merges, one moves potentially from fatal, error to things like note, ignore.