mesa/sso: Add extension entry points for GL_ARB_separate_shader_objects

mesa/sso: Add extension entry points for GL_ARB_separate_shader_objects

Nothings implemented yet but glProgramUniform* which are mostly a
copy/paste of the older function glUniform*

I create dedicated pipelineobj.[ch] file that will contains function
related to the "new" pipeline container object.

V2: formatting improvement

V3:
* indentation fix
* Update copyright
* Add a comment on ProgramParameteri already present in another extension
* Remove TODO, will be readded on correct patch

V4 (idr):
* Fix dispatch_sanity unit test
* Make extension string available in core profiles (instead of just
  compatibility).
* Trivial reformating

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>