SDL_egl: allow creation of versioned OpenGL contexts with EGL_KHR_create_context

If the EGL extension EGL_KHR_create_context is available, we can use it to
set the core/compatability profile and the minimum OpenGL version.

Use this if it is available to get the context requested by the GL attributes.
Fixes #2611 #2610, Touch events cause crash on Android, thanks Alvin & Sylvain

This bug was introduced on this rev: https://hg.libsdl.org/SDL/rev/dc80dc0bd22e
Disable desktop OpenGL for EGL under Android
Another fix to prevent dereferencing a null window pointer in SDL_mouse.c