Using the approach we already do for some GLES 3.0 functions we can provide a cross-platform,
cross-GL-GLES wrapper for ES 3.0 and 3.1 functions too.

Applications only have to take extra care about the version requests (context version
and version directives in shader code), the rest of their code can stay the same across
desktop/mobile/embedded, even when ES 3 functions are used.

The new functions are placed to a new subclass which is placed between QOpenGLFunctions
and the internal QOpenGLExtensions. This is necessary because, unlike with QOpenGLFunctions,
there is no guarantee that these functions are always available in all configurations.

When running on desktop OpenGL, we resolve as usual. If the OpenGL version contains the
function in question, either in core or as an extension, it will all just work. This is
handy because it does not rely on 4.x extensions like GL_ARB_ESx_compatibility, and so
ES 3.0 functions will be functional on OpenGL 3.x systems too by just setting a 3.x version
number in the QSurfaceFormat.

We will no longer qFatal on broken systems where the driver returns a 3.0 or 3.1 context without
the corresponding functions present. Instead, we show a warning and gracefully fall back to
resolving as usual, via eglGetProcAddress or similar. For functions that are available in ES2 as
an extension this may just work fine.

Added also an example that runs identically both with OpenGL and OpenGL ES 3 and utilizes some
ES 3.0 features like instanced drawing.

[ChangeLog] Added QOpenGLExtraFunctions providing OpenGL ES 3.0 and 3.1 function wrappers in
a cross-platform manner.

Task-number: QTBUG-46161
Change-Id: I9f929eb61946c35c415b178c4d6ab2c1c958684e
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>