Override context creation in GLArea.

This allows forward compatible and debug contexts to be created, and
provides more descriptive exceptions in the case where the context
cannot be created with the requested settings.

src/OpenTK.GLWidget/GLWidget.cs

@@ -109,6 +109,22 @@ namespace OpenTK
             return true;
         }
 
+
+        /// <inheritdoc />
+        protected override GLContext OnCreateContext()
+        {
+            var gdkGLContext = Window.CreateGlContext();
+
+            GetRequiredVersion(out var major, out var minor);
+            gdkGLContext.SetRequiredVersion(major, minor);
+
+            gdkGLContext.DebugEnabled = GraphicsContextFlags.HasFlag(GraphicsContextFlags.Debug);
+            gdkGLContext.ForwardCompatible = GraphicsContextFlags.HasFlag(GraphicsContextFlags.ForwardCompatible);
+
+            gdkGLContext.Realize();
+            return gdkGLContext;
+        }
+
         /// <summary>
         /// Destructs this object.
         /// </summary>