Adding function’s internal parameters name to package-interface.json

[ghivert]

Hi !

Right now, package-interface.json is a way to gather all useful intermations about a package, from documentation to docs to types to functions. They're great, and it's a wonderful way to provide a unique, unified interface in the long run for all toolings and to improve the Developer Experience in general.
By focusing on package-interface, a lot of boring things in other languages (analysis, semantic analysing, etc.) can be completely skipped.

However, as of now, there's no information on the internal functions parameters name. The only useful information we can get is the optional label, but names are erased in the interface.

Adding the names would improve the package interface:

• while they're not part of the public API in the code itself, they can help the user to understand the parameters, because library owners do not always add label.
• even if they're not part of the public API of modules, they're still part of hexdocs. Achieving the same result (for instance, to embed docs without having to rely on hexdocs for example) is not possible right now and should parse the code.

It's also a non-breaking change, because they're an addition only to the package-interface.json, meaning existing code won't break, the new field will just be ignored.

In my opinion, they're a great addition in the same sense than keeping the variables types name would be a great addition (update: fn(msg, model) -> #(model, Effect(msg)) is not more accurate than update: fn(a, b) -> #(a, Effect(b)) from the compiler point of view, yet it's a great addition for readers).