docs: Renormalize older extensions.

docs: Renormalize older extensions.

For older extensions, there is an explanation first and the extension
name in brackets, like that:
    Clamping controls (GL_ARB_color_buffer_float)
I inverted that so we have the extension first and then the explanation
in brackets, like that:
    GL_ARB_color_buffer_float (Clamping controls)

It will help me later to parse the few extensions that use this syntax:
    all drivers that support <GL_extension>

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>