include extras from VCSDependencies

[itcarroll]

conda-lock/conda_lock/pypi_solver.py

Line 316 in e29d5cf

# FIXME: how do deal with extras?

I've noticed that if I have pandas[excel] @ git+... in a pyproject.toml dependency sourced from PyPI, then the extra gets ignored. It seems that

1. the "FIXME" above is the culprit, and
2. both VCSDependency and PoetryVCSDependency accept an extras argument,

so maybe whatever stood in the way before is resolved?