Add diagnostic for unnecessary function capture

[u9g]

Thanks for all the work that has gone into the language and the diagnostics, they truly are amazing!

While going through the tutorial, it occurred to me after I wrote this and then removed the (_) that the function capture was completely unnecessary, but with no warning I'm sure this error exists in a ton of codebases already, and could be easily dealt with with a diagnostic added to the compiler.

  1
  |> int.to_string(_) // <-- (_) is unnecessary and can be removed without changing the meaning of the pipeline
  |> string.repeat(5)
  |> string.drop_left(2)
  |> io.println

[lpil]

This is a great idea! Thank you!

[giacomocavalieri]

I can try and work on this!