localrepo: refactor logic to calculate sharedvfs in separate fn
We will be reusing this in an upcoming patch, so better to refactor it into a
separate function. Also the underlying handling deserves a function of it's own.
Differential Revision: https://phab.mercurial-scm.org/D8909
graft c-ext
graft debian
graft zstd
graft tests
include make_cffi.py
include setup_zstd.py
include zstd.c
include LICENSE
include NEWS.rst