Potentially resolves https://github.com/godotengine/godot/issues/101375
VisualShader now has a has_node_embeds function that runs through it's child nodes to find embedded resources via object properties. Conversion plugin uses this function to catch the error.
More detailed logic to fix 3 errors.
* Using 0 as the default value for 'Saved_type' would cause new Particle, Sky, and Fog shaders to display incorrectly and fail to function.
* Passing Saved_type directly into edit_type_select would cause an error because Saved_Type is not the options button index, and can be out of bounds.
* Restoring some saved Particle types correctly requires also checking the custom mode box
