interop_vaapi: break dependency to EGL to enable vglmem clients to use hardware decoding

This will use extensions from EGL directly into interop_vaapi, instead of using those loaded by EGL.

The only users of those extensions are interop modules, so only interop_vaapi for extension related to EGL integration.

By moving the loading of those extension to the interop, we can have them working even when the OpenGL platform context is provided by the vglmem (vgl.c) module callbacks, allowing hardware acceleration even when using the libvlc OpenGL callbacks.

Filters would likely be using only OpenGL extensions that are already available, but could be using the same mechanism in the worst-case scenario.

This patchset is the EGL equivalent of the same[¹] version merged for WGL.

Refs #25234

Fixes #25256 (closed)