Add declaration overrides for matrix shader properties

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/Matrix2ShaderProperty.cs

             get { return PropertyType.Matrix2; }
         }
 
+        public override string GetPropertyDeclarationString(string delimiter = ";")
+        {
+            return "float2x2 " + referenceName + ";";
+        }
+
         public override INode ToConcreteNode()
         {
             return new Matrix2Node 

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/Matrix3ShaderProperty.cs

             get { return PropertyType.Matrix3; }
         }
 
+        public override string GetPropertyDeclarationString(string delimiter = ";")
+        {
+            return "float3x3 " + referenceName + ";";
+        }
+
         public override INode ToConcreteNode()
         {
             return new Matrix3Node 

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/Matrix4ShaderProperty.cs

             get { return PropertyType.Matrix4; }
         }
 
+        public override string GetPropertyDeclarationString(string delimiter = ";")
+        {
+            return "float4x4 " + referenceName + ";";
+        }
+
         public override INode ToConcreteNode()
         {
             return new Matrix4Node