ExplorerShower.cs

using System.Diagnostics;
using UnityEditor;
using UnityEngine;

[InitializeOnLoad]
public static class ExplorerShower
{
    static ExplorerShower()
    {
        EditorApplication.projectWindowItemOnGUI += OnProjectWindowItemOnGUI;
    }
    
    private static void OnProjectWindowItemOnGUI( 
        string guid, 
        Rect selectionRect 
    )
    {
        var rect = selectionRect;
        rect.width = 20;
        rect.x = selectionRect.xMax - 20;
        if ( GUI.Button( rect, "!" ) )
        {
            var assetPath = AssetDatabase.GUIDToAssetPath( guid );
            assetPath = assetPath.Replace( "/", "\\" );
            Process.Start( "explorer.exe", "/select," + assetPath );
        }
    }
}