Improve create undefined function quick action

[plux]

Description

• Create function right after current function
• Create function with correct number of arguments
• Don't leave trailing whitespaces
• Don't create -spec

Fixes #1280

[robertoaloi]

Nice, thanks. Why not to leave the specs (e.g. as any())?

[plux]

None of the codebases I've worked with (except erlang_ls..) enforces -specs on non-exported functions, so adding the -spec is just causing clutter in my opinion.
Adding an incomplete -spec seems pointless to me, and we already have the suggest spec feature which can add a specs
I guess we could add a code action to add missing spec if there is such a diagnostic.

I could add it back if you want to, but my preference is to not add it.

[michalmuskala]

Adding a spec with just any() would be actually worse than no spec at all. AFAIK Dialyzer reports worse errors in cases like that since it interferes with its inference logic.

[robertoaloi]

Fair enough, let's get this one as-is. Yes, the quick action would actually be amazing.