Parameterize InstallRequirement.install_editable
Parameterize InstallRequirement.install_editable

This makes it easier to extract the function without keeping references
to InstallRequirement.

pradyunsg/pip,xavfernandez/pip,sbidoul/pip,pypa/pip,pfmoore/pip,pradyunsg/pip,xavfernandez/pip,pypa/pip,xavfernandez/pip,pfmoore/pip,sbidoul/pip