docs: Renormalize some extensions.

docs: Renormalize some extensions.

This fixes some exceptions I have to deal with in mesamatrix.net.
The extensions GL_ARB_texture_buffer_object had a comment between "DONE"
and the brackets.
And the extension GL_KHR_robustness (in GL 4.5 and GLES 3.1) was using
"90% done" instead of "in progress". The "90% done" is still here
though, but as an extension comment.

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