Refactor npm/yarn invocations

[Turbo87]

We currently have at least three areas of code where npm (and yarn) are used to install dependencies:

• ember install (and ember new, ember addon and ember init) via NpmInstallTask class
• Blueprint.addPackagesToProject()
• InstallBlueprintTask class if the blueprint comes from npm (see Support npm packages as ember new blueprints #6789)

We should try to refactor those code paths to reduce the duplication and use the same code underneath. In the same refactoring the InstallBlueprintTask class needs to be taught about yarn.

see also #6784

[rwjblue]

Don't forget about our test helper which was intended to abstract away these differences: https://github.com/ember-cli/ember-cli/blob/master/tests/helpers/package-cache.js

[g13013]

is there anyone working on this ?

[gnclmorais]

I’m looking into this, hopefully I can come up with something 🙋‍♂️

[gnclmorais]

Hey team! I started working on it (progress at #9789) but got to the point where I would like to know/brainstorm exactly where do we want to take this. What is the ideal outcome of it? How much refactor/DRYness do we want in the code? How much abstraction do we want for install and etc.? Thanks in advance 🙇‍♂️