docs: update trademark disclaimer

It's a *long* time since SGI was the copyright holder for the OpenGL
trademark. And we implement more APIs by now, so let's update the
disclaimer to instead redirect to the Khronos licensing page for
details.

While we're at it, soften the language on legal status as a formal
implementation, as we currently have conformant drivers for most of the
APIs by now. But refer to the Khronos website for details, as
conformance status for drivers are subject to change.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13833>

docs/license.rst

@@ -4,21 +4,21 @@ License and Copyright
 Disclaimer
 ----------
 
-Mesa is a 3-D graphics library with an API which is very similar to that
-of `OpenGL <https://www.opengl.org/>`_ [1]_.
-To the extent that Mesa utilizes the OpenGL command syntax or state
-machine, it is being used with authorization from `Silicon Graphics,
-Inc. <https://www.sgi.com/>`__\ (SGI). However, the author does not
-possess an OpenGL license from SGI, and makes no claim that Mesa is in
-any way a compatible replacement for OpenGL or associated with SGI.
-Those who want a licensed implementation of OpenGL should contact a
-licensed vendor.
+Mesa implements various APIs, including `OpenGL`_, `OpenGL ES`_,
+`Vulkan`_ and `OpenCL`_. Even though Mesa implements these APIs, the
+implementation isn't formally conformant on all combinations of drivers
+and hardware. `Khronos`_ maintains lists of conformant implementations
+for each of their APIs, as well as `trademark details`_.
 
 Please do not refer to the library as *MesaGL* (for legal reasons). It's
 just *Mesa* or *The Mesa 3-D graphics library*.
 
-.. [1] OpenGL is a trademark of `Silicon Graphics
-       Incorporated <https://www.sgi.com/>`__.
+.. _OpenGL: https://www.opengl.org/
+.. _OpenGL ES: https://www.khronos.org/opengles/
+.. _Vulkan: https://www.vulkan.org/
+.. _OpenCL: https://www.khronos.org/opencl/
+.. _Khronos: https://www.khronos.org/
+.. _trademark details: https://www.khronos.org/legal/trademarks/
 
 License / Copyright Information
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