Changes

Bug 1176: BCM VC IV: Refine clamping of window position and size at native creation

- Refines commit a566a1b5a2828b38f1a5c4dfb215ab9b03e7acaa

- Issue clamping at 'canCreateNativeImpl()' instead of 'createNativeImpl()',
  allowing to define clamped position and size before utilizing these values
  at caller 'createNative()'.
  Otherwise a clamped position would cause to wait for the original position
  after 'createNativeImpl()'.

  This also allows to remove the positionChanged(..) / sizeChanged(..) calls in
  the native CreateWindow0() implementation.