Let master node to have 2D preview

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Presenters/NodePreviewPresenter.cs

 
                 List<PropertyGenerator.TextureInfo> defaultTextures;
                 var resultShader =  ((IMasterNode) m_Node).GetFullShader(GenerationMode.Preview, out defaultTextures);
-                m_GeneratedShaderMode = PreviewMode.Preview3D;
+
+                if (((IMasterNode)m_Node).has3DPreview())
+                {
+                    m_GeneratedShaderMode = PreviewMode.Preview3D;
+                }
+                
                 return resultShader;
             }
             return ShaderGenerator.GeneratePreviewShader(m_Node, out m_GeneratedShaderMode);

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Interfaces/IMasterNode.cs

         string GetSubShader(GenerationMode mode, PropertyGenerator shaderPropertiesVisitor);
 
         string GetVariableNameForNode();
+
+        bool has3DPreview();
     }
 }

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Nodes/AbstractMasterNode.cs

 
         public abstract string GetFullShader(GenerationMode mode, out List<PropertyGenerator.TextureInfo> configuredTextures);
         public abstract string GetSubShader(GenerationMode mode, PropertyGenerator shaderPropertiesVisitor);
+
+        public virtual bool has3DPreview()
+        {
+            return true; 
+        }
     }
 }