Support for PEP 808 (partially dynamic metadata)

See [PEP 808](https://peps.python.org/pep-0808/), which was just [accepted](https://discuss.python.org/t/pep-808-partially-dynamic-project-metadata/104883/39). Congrats, nice work @henryiii!

This depends on `pyproject-metadata` gaining support first, see PR https://github.com/pypa/pyproject-metadata/pull/241. Once that is available, we can add support in `meson-python`. 