Support "Fill labels" code action if there are already arguments provided

[joshi-monster]

The language server supports a "add labels" code action, but only if there are no explicit arguments provided:

before:

fn wibble(a a: Int, b b: Float, c c: String) {
  a + b + c
}

fn wobble() {
  wibble()
  //    ^
}

after:

fn wobble() {
  wibble(a: todo, b: todo, c: todo)
}

It would be great if this code action could also support cases where I already partially supply arguments to a function or record constructor. This would be really useful if I added a new argument(s) or field(s), and I want to now update all the call-sides with the new arguments. This code action could add the missing labels for me, so I would have to just fill out the values. ~ 💜

[lpil]

Sounds good!

[giacomocavalieri]

This was not implemented at first because I couldn't figure out how to do it... good news is, fixing #4122 I have figured out how to do it. Once #4131 it should be pretty easy to fix this, I'm working on it!