egl: store the native surface pointer in struct _egl_surface
Each platform stores this in a different place:
- platform_drm uses dri2_surf->gbm_surf->base
- platform_android uses dri2_surf->window
- platform_wayland uses dri2_surf->wl_win
- platform_x11 uses dri2_surf->drawable
- platform_x11_dri3 uses dri3_surf->loader_drawable.drawable
- haiku doesn't even store it!
We need access to the native surface since the specification asks us
to refuse creating a new surface if there's already an EGLSurface
associated with native_surface.
An alternative to this patch would be to create a new
API.GetNativeWindow callback that each platform would have to
implement. While that's something we can definitely do, I prefer
this approach.
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>