compiler, runtime: Refactor P4Type to P4QualifiedType

Also, refer to the different pieces of the qualified type as
qualifiers and not attributes.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/Common/FFI.swift

@@ -17,6 +17,6 @@
 
 public protocol P4FFI {
   func execute(execution: ProgramExecution) -> (ControlFlow, ProgramExecution)
-  func type() -> P4Type
+  func type() -> P4QualifiedType
   func parameters() -> ParameterList
 }