Using `gc+phases+refs=debug`, one will get logs like:

```
   SoftReference:
     Discovered: 998420
     Cleared: 998420
   WeakReference:
     Discovered: 147
     Cleared: 147
   FinalReference:
     Discovered: 0
     Cleared: 0
   PhantomReference:
     Discovered: 2
     Cleared: 2
```

The word "Cleared" can be interpreted as `ref.referent = null`, but what this metric actually tracks is #refs dropped (referent == null or reachable) from the discovered list (DL).

Improve the wording to make it more accurate and make the output more compact.