[WIP] u3d/installation: add feature to create shortcuts

[niezbop]

Pull Request Checklist

• [x] My pull request has been rebased on master
• [x] I ran bundle exec rspec to make sure that my PR didn't break any test
• [x] I ran bundle exec rubocop to make sure that my PR is inline with our code style
• [x] I have read the code of conduct

Pull Request Description

This brings a small QoL improvement which enables one to create shortcuts for his Unity installs in any directory.

Relies on the win32-shortcut gem.

[lacostej]

Some questions

• How does this windows specific dependency affects other platforms? is this tested on non Windows?
• We could envision supporting other platforms, in which case we would have the same feature on Mac / Linux. In that case I would feel that we could move the platform specific dependencies in a class specific to the shortcut creation maybe.
• tests!

More comments in the review itself.