Implement input name evaluation. Implement context state.

Assets/Cryville/Crtr/PropSrc.cs

@@ -56,6 +56,14 @@ namespace Cryville.Crtr {
 				}
 			}
 		}
+		public class Identifier : PropSrc {
+			readonly Func<int> _cb;
+			public Identifier(Func<int> cb) { _cb = cb; }
+			protected override void InternalGet(out int type, out byte[] value) {
+				type = PdtInternalType.Undefined;
+				value = BitConverter.GetBytes(_cb());
+			}
+		}
 		public class BeatTime : PropSrc {
 			readonly Func<RBeatTime> _cb;
 			public BeatTime(Func<RBeatTime> cb) { _cb = cb; }