Fix indention formatter for google.protobuf.Any (#16785)

`google.protobuf.Any` formatting with indentation was somewhat off.

Formatting an `Any` as root object:
```json
{"@type": "type.googleapis.com/protobuf_unittest3.ForeignMessage",
"c": 1
}
```
changes to
```json
{
  "@type": "type.googleapis.com/protobuf_unittest3.ForeignMessage",
  "c": 1
}
```

For messages were `Any` is in a nested field the change makes more of a visual impact.
The `c` field seems to be at the same level as the `anyField`, but it's nested so it should be indented:
```json
{
  "anyField": {"@type": "type.googleapis.com/protobuf_unittest3.ForeignMessage",
  "c": 1
  }
}
```
changes to:
```json
{
  "anyField": {
    "@type": "type.googleapis.com/protobuf_unittest3.ForeignMessage",
    "c": 1
  }
}
```

Closes #16785

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/16785 from q42jaap:main 72deed6ed774c3206b5a4e925d7c58c114cb2537
PiperOrigin-RevId: 632506226