Refactor Support*Order to inherit from abstract SupportOrder

MultiversalDiplomacy/Orders/SupportHoldOrder.cs

@@ -5,16 +5,10 @@ namespace MultiversalDiplomacy.Orders;
 /// <summary>
 /// An order for a unit to support another unit's hold order.
 /// </summary>
-public class SupportHoldOrder : UnitOrder
+public class SupportHoldOrder : SupportOrder
 {
-    /// <summary>
-    /// The unit to support.
-    /// </summary>
-    public Unit Target { get; }
-
     public SupportHoldOrder(Power power, Unit unit, Unit target)
-        : base (power, unit)
+        : base (power, unit, target)
     {
-        this.Target = target;
     }
 }

MultiversalDiplomacy/Orders/SupportMoveOrder.cs

@@ -5,13 +5,8 @@ namespace MultiversalDiplomacy.Orders;
 /// <summary>
 /// An order for a unit to support another unit's move order.
 /// </summary>
-public class SupportMoveOrder : UnitOrder
+public class SupportMoveOrder : SupportOrder
 {
-    /// <summary>
-    /// The unit to support.
-    /// </summary>
-    public Unit Target { get; }
-
     /// <summary>
     /// The destination season to which the target is moving.
     /// </summary>
@@ -23,9 +18,8 @@ public class SupportMoveOrder : UnitOrder
     public Location Location { get; }
 
     public SupportMoveOrder(Power power, Unit unit, Unit target, Season season, Location location)
-        : base (power, unit)
+        : base(power, unit, target)
     {
-        this.Target = target;
         this.Season = season;
         this.Location = location;
     }

MultiversalDiplomacy/Orders/SupportOrder.cs

@@ -0,0 +1,20 @@
+using MultiversalDiplomacy.Model;
+
+namespace MultiversalDiplomacy.Orders;
+
+/// <summary>
+/// An order for a unit to support another unit.
+/// </summary>
+public abstract class SupportOrder : UnitOrder
+{
+    /// <summary>
+    /// The unit to support.
+    /// </summary>
+    public Unit Target { get; }
+
+    public SupportOrder(Power power, Unit unit, Unit target)
+        : base (power, unit)
+    {
+        this.Target = target;
+    }
+}