Create a helper function that will install a project from local cache

The entire UI is being removed from update.module. I'm tempted to close this is outdated. There's no need to have a helper function to share code, project browser is the only thing that will need it.

I agree this seems pretty outdated, since modern Project Browser will not (as the current issue summary says, "[rely] on the update module to fetch and install projects from Drupal.org").

Using Package Manager to install packages into the codebase using Composer is the de facto library for doing those operations moving forward, as far as I understand it as initiative lead from Project Browser.

Agree with #27 this is outdated