Remove the Gdk.Key enum now that the constants from gir.core can be used

Gdk.Key is now just a wrapper type around the uint key value for better type safety

Pinta.Core/Classes/BaseTool.cs

@@ -118,10 +118,11 @@ public virtual IEnumerable<IToolHandle> Handles
 		=> Enumerable.Empty<IToolHandle> ();
 
 	/// <summary>
-	/// The shortcut key used to activate this tool in the toolbox. Return 0 for no shortcut key.
+	/// The shortcut key used to activate this tool in the toolbox.
+	/// Return Gdk.Key.Invalid for no shortcut key.
 	/// </summary>
 	public virtual Gdk.Key ShortcutKey
-		=> 0;
+		=> Gdk.Key.Invalid;
 
 	/// <summary>
 	/// Affects the order of the tool in the toolbox. Lower numbers will appear first.

Pinta.Core/Extensions/GdkExtensions.cs

@@ -66,17 +66,6 @@ public static bool IsLeftMousePressed (this Gdk.ModifierType m)
 	public static bool IsRightMousePressed (this Gdk.ModifierType m)
 		=> m.HasFlag (Gdk.ModifierType.Button3Mask);
 
-	/// <summary>
-	/// Returns whether this key is a Ctrl key (or the Cmd key on macOS).
-	/// </summary>
-	public static bool IsControlKey (this Gdk.Key key)
-	{
-		if (PintaCore.System.OperatingSystem == OS.Mac)
-			return key == Gdk.Key.Meta_L || key == Gdk.Key.Meta_R;
-		else
-			return key == Gdk.Key.Control_L || key == Gdk.Key.Control_R;
-	}
-
 	/// <summary>
 	/// Returns whether any of the Ctrl/Cmd/Shift/Alt modifiers are active.
 	/// This prevents Caps Lock, Num Lock, etc from appearing as active modifier keys.
@@ -185,14 +174,6 @@ public static Gdk.Texture CreateIconWithShape (
 		return Gdk.Texture.NewForPixbuf (i.ToPixbuf ());
 	}
 
-	public static Gdk.Key ToUpper (this Gdk.Key k1)
-	{
-		if (Enum.TryParse (k1.ToString ().ToUpperInvariant (), out Gdk.Key result))
-			return result;
-		else
-			return k1;
-	}
-
 	// TODO-GTK4 (bindings, unsubmitted) - need gir.core async bindings for Gdk.Clipboard
 	public static Task<Gdk.Texture?> ReadTextureAsync (this Gdk.Clipboard clipboard)
 	{