Support for PEP 808 (partially dynamic metadata)

[rgommers]

See PEP 808, which was just accepted. Congrats, nice work @henryiii!

This depends on pyproject-metadata gaining support first, see PR pypa/pyproject-metadata#241. Once that is available, we can add support in meson-python.

[QuLogic]

Oh, will this PEP mean we can finally get correct license files (based on enabled subproject configuration)?

[rgommers]

I think yes - or at least, more correct (the auditwheel et al. vendoring part of it is still missing). Licensing is an explicit use case in the PEP: "Adding license files to the wheel based on what libraries are linked in (this is an active discussion in follow-up to PEP 639)."

[henryiii]

FYI, see https://discuss.python.org/t/dynamic-metadata-the-package/107953, I'll probably try adding support for dynamic-metadata here soonish.