Inline polymorphic functions

[jrudolph]

Beta reduction currently only supports non-polymorphic function inlining:

inline def f[T](inline t: T, inline g: T => T): T = g(t)
f("test", identity)
// result:
// {
//    val x$proxy1: String = "test"
//    identity[String](x$proxy1)
//  }:String

inline def fpoly(inline g: [T] => T => T): String = g("blup")
fpoly([T] => (x: T) => identity[T](x))
// result:
// {
//   final class $anon() extends Object(), PolyFunction {
//     def apply[T >: Nothing <: Any](x: T): T = identity[T](x)
//   }
//   (new $anon():PolyFunction{apply: [T](x: T): T})
// }.apply[String]("blup"):String