Desktop text controls retain selections after focus changes

Desktop TextField, TextArea, and SearchField selections disappear when the control loses focus. Selecting text and then tabbing to another control, showing a message box, or switching away from the app can leave SelectionLength at zero and SelectedText empty when the user returns. This also prevents an app from saving and restoring the user's selected range after focus has moved. The selected range should remain available until the user changes the text or selection.