Add support for SCI_GETFOCUS and SCI_SETFOCUS

src/ScintillaNET/Scintilla.cs

@@ -4287,6 +4287,25 @@ public int IndicatorValue
             }
         }
 
+        /// <summary>
+        /// This is used by clients that have complex focus requirements such as having their own window
+        /// that gets the real focus but with the need to indicate that Scintilla has the logical focus.
+        /// </summary>
+        [Browsable(false)]
+        [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
+        public bool InternalFocusFlag
+        {
+            get
+            {
+                return (DirectMessage(NativeMethods.SCI_GETFOCUS) != IntPtr.Zero);
+            }
+            set
+            {
+                var focus = (value ? new IntPtr(1) : IntPtr.Zero);
+                DirectMessage(NativeMethods.SCI_SETFOCUS, focus);
+            }
+        }
+
         /// <summary>
         /// Gets or sets the current lexer.
         /// </summary>