Give menus of lookup widgets correct width and text size

Problems:
* The width being set in OO.ui.TextInputMenuWidget was being overridden
  in OO.ui.ClippableElement
* The menu was being added to the body instead of the overlay div when
  inside an OO.ui.Window

Solutions:
* Add ideal size information to OO.ui.ClippableElement rather than
  hardcoding fallbacks for width and height as attribute removals
* Default $overlay to .oo-ui-window-overlay if present, ensuring correct
  placement in OO.ui.Window without changing default placement in other
  cases

Change-Id: I16638f40f287e02fb1f59e262635419819eb517c