Use EGL symbols from EGL library directly instead of loading through vlc_gl_GetProcAddress. In the future, we might want to use runtime loading through the egl provider capabilities but it's currently unused and loading EGL through GLX (vlc_gl_GetProcAddress) is leading to undefined results and crash.
With this patch, the interop_vaapi correctly fails when running with GLX and it falls back on EGL to load the interop.
Fixes #26813