What's the problem this feature will solve?

With PEP 639 accepted, there is a new metadata field to get the license information from: License-Expression.

pip show currently shows the License field contents:

Describe the solution you'd like

I think should add the display of License-Expression field and in the long run maybe switch to it entirely. Initially there will be a few packages produced with the new metadata, but in the long run only the License-Expression will remain.
Hence, I'd propose to try to obtain the license information from License-Expression - standardized and validated and fall back to the deprecated unstructured License in case License-Expression isn't found.

Alternative Solutions

What else is possible:

• do nothing - the deprecated License will be less used in time
• switch to License-Expression entirely - for majority of existing packages this would mean producing an empty field for months/years to come
• add License-Expression as a separate field displayed with the package data - this feels redundant, but if that's deemed a better approach, I'm not against.

Additional context

Once agreed upon solution, I can send a patch.

Code of Conduct

• I agree to follow the PSF Code of Conduct.