conda pypi install -e . --prefix=<prefix> fails with missing editables package #281

Checklist

• I added a descriptive title
• I searched open reports and couldn't find a duplicate

What happened?

When trying to do an editable install of conda, conda-pypi fails with a missing editables package used to build the editable wheel.

conda-pypi may not be installing the get-requires-for-build-editable packages at the right time or into the right environment.

Additional Context

From testing, conda pypi install --prefix /tmp/conda editables into the target prefix allows the original command to work.

Note that it has to be the discovered dependencies from the Python build hook, not necessarily the editables package and possibly a version-constrained editables package.