Record the underlying native display instance into the toplevel
GstVaapiDisplay object. This is useful for fast lookups to the
underlying native display, e.g. for creating an EGL display.
Add new generic helper functions gst_vaapi_texture_new_wrapped()
and gst_vaapi_texture_new() to create a texture without having
the caller to uselessly check for the display type himself. i.e.
internally, there is now a GstVaapiDisplayClass hook to create
textures, and the actual backend implementation fills it in.
This is a simplification in view to supporting EGL.
GstVaapiTexture is a generic abstraction that could be moved to the
core libgstvaapi library. While doing this, no extra dependency needs
to be added. This means that a GstVaapitextureClass is now available
for any specific code that needs to be added, e.g. creation of the
underlying GL texture objects, or backend dependent ways to upload
a surface to the texture object.
Generic OpenGL data types (GLuint, GLenum) are also replaced with a
plain guint.
https://bugzilla.gnome.org/show_bug.cgi?id=736715
