[client] egl: properly use OpenGL ES

Instead of using the desktop <GL/gl.h>, we properly use the OpenGL ES 3.x
headers. Also, we now use GL_EXT_buffer_storage for MAP_PERSISTENT_BIT_EXT
and MAP_COHERENT_BIT_EXT as the core versions are only available in desktop
OpenGL 4.4. Similarly, we need GL_EXT_texture_format_BGRA8888 for GL_BGRA_EXT
as GL_BGRA is desktop-only.

client/include/egl_dynprocs.h

@@ -23,7 +23,8 @@
 #ifdef ENABLE_EGL
 
 #include <EGL/egl.h>
-#include <GL/gl.h>
+#include <GLES3/gl3.h>
+#include <GLES2/gl2ext.h>
 
 typedef EGLDisplay (*eglGetPlatformDisplayEXT_t)(EGLenum platform,
     void *native_display, const EGLint *attrib_list);