Global dependency installs for virtual environment

I know it's not really the done thing, but I use a virtual environment ([nodeenv](https://github.com/ekalinin/nodeenv)) for my projects, and would very much like to have the option not to have a `/node_modules` folder, but instead have required packages installed with the global flag. This would actually install them to my virtual environment.

Is there a way of doing this? If not, could the option be added?

The issue mentions nodeenv, /node_modules, and global package installation but names no Ionic CLI files or tests. Start by locating the CLI's dependency-installation entry point and existing option coverage; done would be a documented option that installs required packages into the virtual environment and has tests for that behavior.

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