Improve stability of lambda implementation method name

[retronym]

We ought to include the enclosing method name in the method name.

Starting with:

class C {
  var a = 5
  def foo() {
    val f1 = () => a.toString
    val f2 = (x: Int) => x * a
    val f3 = (z: String) => s"$z$a$z"
  }
}

To:

class C {
  var a = 5
  def bar() {
     () => ()
  }
  def foo() {
    val f1 = () => a.toString
    val f2 = (x: Int) => x * a
    val f3 = (z: String) => s"$z$a$z"
  }
}

Ought to be a serialization compatible change.

[SethTisue]

this would help make stack traces more readable, too.

[retronym]

https://github.com/scala/scala/compare/2.12.x...retronym:topic/trait-statics?expand=1

class C { () => ""; def foo = {def local = () => ""; local}; def bar = () => foo; def baz = () => C.this }
Compiled from "test.scala"
public class C {
  public scala.Function0<java.lang.String> foo();
  public scala.Function0<scala.Function0<java.lang.String>> bar();
  public scala.Function0<C> baz();
  public static final java.lang.String $anonfun$new$1();
  public static final java.lang.String $anonfun$foo$1();
  private final scala.Function0 local$1();
  public static final scala.Function0 $anonfun$bar$1(C);
  public static final C $anonfun$baz$1(C);
  public C();
  private static java.lang.Object $deserializeLambda$(java.lang.invoke.SerializedLambda);
}

[lrytz]

fixed by scala/scala#5157