Improve "generate interface stubs" interface

[Ackar]

This improves the interface for the "generate interface stubs" command as per #1823.
This adds a way to select a package and interface as well as automatic receiver name generation.

Example usage:

I couldn't find a way to list interfaces from a package with the current tools so I added my own, but I'd be happy to change that if I missed something.

[msftclas]

All CLA requirements met.

[kunzeal]

@Ackar Any progress of this? Looking forward to it.

[Ackar]

I'm just waiting for review 🙂

@ramya-rao-a Any thoughts on this? I'm happy to make any changes if needed.

[pankrator]

Any chances of getting this nice functionality soon?

[ramya-rao-a]

Hello all, thanks for your patience

@stamblerre, @hyangah Are you aware of any existing Go tools that can list interfaces from a given package?

[ramya-rao-a]

Hello all,

We would prefer a solution where we don't have to add a dependency on yet another Go tool that will have to be shelled out from the extension. Moreover, as mentioned in #1823 (comment), further development on the stubbing interfaces is being explored via gopls. See golang/go#37537.

Therefore, closing this PR.

Thanks for all your efforts here.
I'd like to encourage people who upvoted this PR and looking forward to this change to subscribe to golang/go#37537 and take part in the discussion there.