macosx: Refactor setupVoutForWindow in VLCVideoOutputProvider

This PR's main changes regarding setupVoutForWindow are:

1. It moves much of the introspection into mainInstance.libraryWindow out of VLCVideoOutputProvider and into VLCLibraryWindow, where the actions that need doing to setup/unsetup video playback called by the setter of hasActiveVideo (which we always call regardless of the video window type)
2. It moves the creation of the borderless window (video wallpaper / no decoration window) into its own function, reducing the complexity of setupVoutForWindow
3. Cleans up redundant conditional cases and unnecessary assignments

Signed-off-by: Claudio Cambra claudio.cambra@gmail.com