DX9AllocatorPresenter: Use a focus window in D3DFullscreen.

Also, don't allow D3D to change the window style. This fixes the loss of focus when D3DFullscreen is active.
Exit fullscreen if focus is changed to a window on the same monitor even with multi-monitor setups.

This commit reverts 7e22ddca36d0556f8ef30cc8cae1aab40b746cba.