Request: read version from .git_archival.txt

[whitequark]

When you generate an archive from a release using git archive (or download it from GitHub), there is no .git and tags are not available. However, it is possible to get git archive to put the necessary information into a file with substitutions defined, .git_archival.txt, as used in setuptools_scm.

Would it be possible to implement the same mechanism in pdm-backend? This is the only item holding off my migration from setuptools build backend at the moment.