Add --no-require-hashes (#14186)

which disables the automatic enforcement of hashes when any requirement
with a --hash is encountered. This enables hashed requirements to be
mixed with directory and VCS requirements, notably editable
requirements.

It was seemed too risky to simply remove the automatic enablement of
--require-hashes as it was originally designed this way to avoid
non-hashed requirements from leaking into a pip install. While this
is a dubious design decision, the ship has sailed a long time ago.