EGLDisplay & EGLSurface GL targets satisfaction in SDL3

[hermet]

@wenjieshen We might need to upgrade to SDL3 first. Until that, we could pass nullptr...

SDL_EGLDisplay display = SDL_EGL_GetCurrentDisplay();
 // sdl is running on egl.
if (display) {
   //get surface
}

https://wiki.libsdl.org/SDL3/SDL_EGL_GetCurrentDisplay
https://wiki.libsdl.org/SDL3/SDL_EGL_GetWindowSurface

Originally posted by @hermet in thorvg/thorvg.example#10 (comment)