opengl: interop: refactor to use the vlc_gl_interop API

Provides the vlc_gl_interop object as parameter to the activate function for the modules, instead of a generic vlc_object_t. This removes the need for casting the vlc_object_t and clarify how interop modules are loaded.

The new activation function will also allow to supply new parameters in the future, and the vlc_gl_interop API is used instead of the module API.