android: add a new file in order to refactor common code between Android vout modules.

Implement a function to load the Native Window API from the Android
library.  This API is needed by current vouts nativewindow and surface
and will also be needed by the opaque vout.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
android: use common function LoadNativeWindowAPI instead of duplicating code in vout modules.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>