opengl: remove refcounting and move vtable from core to modules
The refcounting API has never been used, and is fundamentally useless with the removal of the reference counting pattern in objects.
Indeed, the OpenGL providers are neither multi-thread nor reentrant so it needs a locked stated when multiple clients needs to use it, which will also needs to be reference counted across the clients, so the whole reference counting can be done there.
In addition, if the context was given from module to other module, like in the filter chain, the video contexts forwarded in those chains would already be doing the reference counting. As a side note, there would probably be few reasons to implement such forwarding currently anyway since it would means that the beginning of the chain would lose usage of the context, which also encompass a pool of output picture too currently.
Also move the opengl vtable for checking extensions to the modules, where the other OpenGL helpers are and OpenGL types are available.
Fix #26606 (closed)