[augmentations] Wrong analyzer warning when augmenting enum constructor

[sgrekhov]

The code below produces a warning in the analyzer (with --enable-experiment=macros).

enum E {
  e0(0), e1.foo();
  final int x;
  const E(this.x);
  const E.foo(): this(1); //  The declaration 'E.foo' isn't referenced. Try removing the declaration of 'E.foo'. • unused_element
}

augment enum E {
  e2(1);
  augment const E.foo();
}

main() {
  print(E.e1);
}

E.foo() is referenced here so the warning is wrong.

Dart SDK version: 3.7.0-86.0.dev (dev) (Wed Oct 30 17:03:22 2024 -0700) on "windows_x64"