Add support for Metadata 2.2 (#2293)
## Summary
PyPI now supports Metadata 2.2, which means distributions with Metadata
2.2-compliant metadata will start to appear. The upside is that if a
source distribution includes a `PKG-INFO` file with (1) a metadata
version of 2.2 or greater, and (2) no dynamic fields (at least, of the
fields we rely on), we can read the metadata from the `PKG-INFO` file
directly rather than running _any_ of the PEP 517 build hooks.
Closes https://github.com/astral-sh/uv/issues/2009.
