[opengl-registry,vcpkg-spdx] Get missing license info from SPDX

[dg0yt]

• What does your PR fix?

  Fixes improper copyright in opengl-registry. For this purpose, adds a script port / maintainer function which gives access to the SPDX license list data.

[Cheney-W]

Since the MIT and Apache-2.0 has been added into the copyright of opengl-registry, should the "license" field be added to ports/opengl-registry/vcpkg.json?

[dg0yt]

Done.

[dg0yt]

FTR there are spdx-license-list-data packages in other repositories. https://repology.org/project/spdx-license-list-data/information

But I don't see a point in transforming the original source asset into a nearly identical binary artifact. W.r.t. vcpkg, the only relevance is in providing license data at port build time.

[BillyONeal]

Maybe we should resolve this by supplying license text, but also requiring some form of verification e.g. some file in the original we check for a string inside like "released under the foo license" so that should that change we know?

[moritz-h]

In #36856 I noted the same license mix applies to the egl-registry port, just with a few less files and licenses. Further opengl-registry not only mixes MIT and Apache-2.0, but several files include other individual licenses, e.g., api/GLSC/1.0/gl.h or api/GLES/1.0/gl.h