SI-9871 infer higher-order function argument types from overloaded method if argument types agree (fix source incompat introduced by sammy)

[adriaanm]

Overloaded method with argument of function type --> ok as long as argument types derived from lub of function types agree:

def map(f: Char => A)
def map(f: Char => Char)

fails now, but could be made to work (would fix sam breaking overloads, and align with dotty)

[adriaanm]

see #125 (dupe) for example:

trait Bijection[A, B] extends (A => B) {
   def andThen[C](g: Bijection[B, C]): Bijection[A, C] = ???
   def compose[T](g: Bijection[T, A]) = g andThen this
}

// <console>:14: error: overloaded method compose needs result type
// def compose[T](g: Bijection[T, A]) = g andThen this
//                                        ^

adriaanm/util@78f8eef

[retronym]

See also: https://issues.scala-lang.org/browse/SI-9871