[Torque] Provide a specialization of Cast<Context|Zero|Undefined>

Bug: v8:11727
Change-Id: Id78995e250e16f43687db1c7ce97a59c635b5424
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2871459
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74358}

src/builtins/cast.tq

@@ -329,6 +329,24 @@ Cast<Number|TheHole>(o: Object): Number|TheHole labels CastError {
   }
 }
 
+Cast<Context|Zero|Undefined>(o: Object): Context|Zero|Undefined
+    labels CastError {
+  typeswitch (o) {
+    case (o: Context): {
+      return o;
+    }
+    case (o: Zero): {
+      return o;
+    }
+    case (o: Undefined): {
+      return o;
+    }
+    case (Object): {
+      goto CastError;
+    }
+  }
+}
+
 macro Cast<A : type extends HeapObject>(o: HeapObject): A
     labels CastError;