Fix system file dialog not opening on *nix systems

Built-in commands "show_game_files" and "show_data_files" now open
system file dialogs for *nix based systems. The fix is system-agnostic
and works on Windows as well.

Resolves: #851

src/SMAPI.Mods.ConsoleCommands/Framework/Commands/Other/ShowDataFilesCommand.cs

@@ -20,7 +20,12 @@ public ShowDataFilesCommand()
         /// <param name="args">The command arguments.</param>
         public override void Handle(IMonitor monitor, string command, ArgumentParser args)
         {
-            Process.Start(Constants.DataPath);
+            Process.Start(new ProcessStartInfo
+            {
+                FileName = Constants.DataPath,
+                UseShellExecute = true
+            });
+
             monitor.Log($"OK, opening {Constants.DataPath}.", LogLevel.Info);
         }
     }

src/SMAPI.Mods.ConsoleCommands/Framework/Commands/Other/ShowGameFilesCommand.cs

@@ -20,7 +20,12 @@ public ShowGameFilesCommand()
         /// <param name="args">The command arguments.</param>
         public override void Handle(IMonitor monitor, string command, ArgumentParser args)
         {
-            Process.Start(Constants.GamePath);
+            Process.Start(new ProcessStartInfo
+            {
+                FileName = Constants.GamePath,
+                UseShellExecute = true
+            });
+
             monitor.Log($"OK, opening {Constants.GamePath}.", LogLevel.Info);
         }
     }