compiler, runtime, common, testing: Support Directions on Parameters and Attributed Types

Add support for directions on parameters and attributed types. The
latter is necessary to support the former, but is not limited to
the direction use case. An attributed type is a P4 type with attributes
(like its direction, whether it is read only, etc.) Other attributes
will be added in the future.

Changes necessary to support attributed types include:
1. Global instances tracked during compilation are not attributed
types and not simply types.
2. (future) Type checking will have to make sure that a types
attributes do not affect type compatibility.

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

Sources/P4Lang/Types.swift

@@ -14,3 +14,15 @@
 //
 // You should have received a copy of the GNU General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+import Common
+
+public struct AttributedP4Type {
+  public let type: P4Type
+  public let attributes: P4TypeAttributed
+
+  public init(_ type: P4Type, _ attributes: P4TypeAttributed) {
+    self.type = type
+    self.attributes = attributes
+  }
+}