Find a way to share code across completion specs

[QuiiBz]

Is your feature request related to a problem? Please describe.
Based on #288, the yarn and npx specs should share the same CLIs (e.g yarn electron and npx electron. Currently, this would lead to duplication and is not very handy.

Describe the solution you'd like
Having a way to share code like generators, arguments, and more across many completion specs would be really cool. The exact implementation will need to be discussed here.

[mschrage]

I think the current approach would be to include a reference to an external completion spec using loadSpec but open to discussing alternatives (potentially, using imports).

[QuiiBz]

This approach would make it hard to get the correct types of the loaded completion spec. Having the possibility to import and export stuff across completion specs could be awesome, but we will need to update the specs compiler: it currently looks for the first exported variable and assumes that it's the spec object, so that would need to be updated to support many exports.

[fedeci]

We may add an eslint plugin to enforce naming of the completion spec esport.
For example eslint itself (or maybe typescript-eslint🤔) is doing that internally for their rules. I can work on that if needed.

[QuiiBz]

@cstrnt has been working on this in #388 - this is going to be amazing!

[ankithm28]

Closed with #388