[wildcards] Consider quick fix: convert `UNUSED_CATCH_CLAUSE` to wildcard

Specifically,

```dart
f() {
  try {
  } on String catch (exception) {
  }
}
```

_might_ be fixed to:

```dart
f() {
  try {
  } on String catch (_) {
  }
}
```

in addition to the current fix which removes the clause altogether:

```dart
f() {
  try {
  } on String {
  }
}
```

**Question:** does such a fix add value?

@kallentu @bwilkerson 
