SI-9390 Avoid needless outer capture with local classes

An existing optimization in `Constructors` elides the outer
field in member and local classes, if the class doesn't use
the outer reference. (Member classes also need to be final,
which is a secret handshake to say we're also happy to weaken
prefix matching in the pattern matcher.)

That optimization leaves the constructor signature as is: the
constructor still accepts the outer instance, but does not store
it. For member classes, this means that we can separately compile
code that calls the constructor.

Local classes need not be hampered by this constraint, we could
remove the outer instance from the constructor call too.

Why would we want to do this?

Let's look at the case before and after this commit.

Before:
```
class C extends Object {
  def foo(): Function1 = $anonfun();
  final <static> <artifact> def $anonfun$foo$1($this: C, x: Object): Object = new <$anon: Object>($this);
  def <init>(): C = {
    C.super.<init>();
    ()
  }
};
final class anon$1 extends Object {
  def <init>($outer: C): <$anon: Object> = {
    anon$1.super.<init>();
    ()
  }
}
```

After:

```
class C extends Object {
  def foo(): Function1 = $anonfun();
  final <static> <artifact> def $anonfun$foo$1(x: Object): Object = new <$anon: Object>(null);
  def <init>(): C = {
    C.super.<init>();
    ()
  }
};
final class anon$1 extends Object {
  def <init>($outer: C): <$anon: Object> = {
    anon$1.super.<init>();
    ()
  }
}

```

However, the status quo means that a lambda that
This in turn makes lambdas that refer to such classes serializable
even when the outer class is not itself serialiable.

I have not attempted to extend this to calls to secondary constructors.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
index 28222cf9a7..0a90a141d3 100644
--- a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
+++ b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
@@ -45,6 +45,7 @@ trait JavaUniverseForce { self: runtime.JavaUniverse  =>
     this.SubpatternsAttachment
     this.NoInlineCallsiteAttachment
     this.InlineCallsiteAttachment
+    this.OuterArgCanBeElided
     this.noPrint
     this.typeDebug
     this.Range