make Facing's enum value correspond to the x-direction they're looking

GitOrigin-RevId: fe9318a68e

Shared/Player.cs

@@ -4,7 +4,12 @@ using System.Collections.Generic;
 
 namespace SemiColinGames {
   class Player {
-    enum Facing { Left, Right };
+    // The player's Facing corresponds to the x-direction that they're looking.
+    enum Facing {
+      Left = -1,
+      Right = 1
+    };
+
     enum Pose { Walking, Standing, Crouching, Stretching, SwordSwing, Jumping };
 
     private const int moveSpeed = 180;