API changes in Unity 2021.2a19

Unity 2021.2a19 has some API changes that will affect this code:

https://github.com/microsoft/MRDL_Unity_Surfaces/blob/dc3f88b36c7df76f9460280199f551d525028b52/Assets/MixedRealityToolkit/Utilities/Editor/IconEditor.cs#L23

EditorGUIUtility.SetIconForObject/GetIconForObject are now public.
MonoImporter.SetIcon/GetIcon are now public.
PluginImporter.SetIcon/GetIcon are now public.
MonoImporter.CopyMonoScriptIconToImporters is now obsolete and will output a warning to the console when called.

Starting with this version of Unity, MonoImporter.CopyMonoScriptIconToImporters can be replaced with the following:

// given monoScript and icon
var importer = AssetImporter.GetAtPath(AssetDatabase.GetAssetPath(monoScript));
importer.SetIcon(icon);
importer.SaveAndReimport();

microsoft / MRDL_Unity_Surfaces

API changes in Unity 2021.2a19 #6