Refactor GDScript/C# script templates logic to be editor-only

Not a full refactor as it still goes through ScriptLanguage so it's hacky,
but at least it can now compile without this.

modules/mono/editor/script_templates/VisualShaderNodeCustom/basic.cs

@@ -0,0 +1,62 @@
+// meta-description: Visual shader's node plugin template
+
+using _BINDINGS_NAMESPACE_;
+using System;
+
+public partial class VisualShaderNode_CLASS_ : _BASE_
+{
+    public override string _GetName()
+    {
+        return "_CLASS_";
+    }
+
+    public override string _GetCategory()
+    {
+        return "";
+    }
+
+    public override string _GetDescription()
+    {
+        return "";
+    }
+
+    public override int _GetReturnIconType()
+    {
+        return 0;
+    }
+
+    public override int _GetInputPortCount()
+    {
+        return 0;
+    }
+
+    public override string _GetInputPortName(int port)
+    {
+        return "";
+    }
+
+    public override int _GetInputPortType(int port)
+    {
+        return 0;
+    }
+
+    public override int _GetOutputPortCount()
+    {
+        return 1;
+    }
+
+    public override string _GetOutputPortName(int port)
+    {
+        return "result";
+    }
+
+    public override int _GetOutputPortType(int port)
+    {
+        return 0;
+    }
+
+    public override string _GetCode(Godot.Collections.Array inputVars, Godot.Collections.Array outputVars, Shader.Mode mode, VisualShader.Type type)
+    {
+        return "";
+    }
+}