Add Modification API:

- The Modification API is designed specifically for the creation and distribution of modular prefabs, where a developer generates assets on their machine and distributes those generated assets to their users.
  - Add AacFlModification class.
  - Add (AacFlBase).Modification() which returns a AacFlModification.

Packages/dev.hai-vr.animator-as-code.v1/V1/Editor/Aac.cs

@@ -523,13 +523,15 @@ namespace AnimatorAsCode.V1
             return new AacFlClip(_configuration, clip);
         }
         
-        /// Create a new BlendTree asset with a name. However, the name is only used as a suffix for the asset. The asset is generated into the container.
+        /// Create a new BlendTree asset with a name. However, the name is only used as a suffix for the asset. The asset is generated into the container.<br/>
+        /// Added in 1.3.0.
         public AacFlNonInitializedBlendTree NewBlendTree(string name)
         {
             return new AacFlNonInitializedBlendTree(AacInternals.NewBlendTreeAsRaw(_configuration, name));
         }
 
-        /// Create a new BlendTree asset with a name and returns a native BlendTree object. However, the name is only used as a suffix for the asset. The asset is generated into the container. You may use NewBlendTree() instead to obtain a fluent interface.
+        /// Create a new BlendTree asset with a name and returns a native BlendTree object. However, the name is only used as a suffix for the asset. The asset is generated into the container. You may use NewBlendTree() instead to obtain a fluent interface.<br/>
+        /// Added in 1.3.0.
         public BlendTree NewBlendTreeAsRaw(string name)
         {
             return AacInternals.NewBlendTreeAsRaw(_configuration, name);
@@ -640,6 +642,13 @@ namespace AnimatorAsCode.V1
         {
             return new AacFlNoAnimator();
         }
+
+        /// Returns a new AacFlModification instance, granting you access to this destructive modification API. You will need to reuse this object throughout.<br/>
+        /// Added in 1.3.0.
+        public AacFlModification Modification()
+        {
+            return new AacFlModification(_configuration, this);
+        }
     }
 
     public class AacFlNoAnimator