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GH-44101: [C++][Parquet] Tools: Debug Print for Json should be valid JSON (#44532)

### Rationale for this change

The printJson is not a valid json now. This is ok for human-read, but when I want to analysis it with json tools or ai, it will prevent from using it.

### What changes are included in this PR?

Change the output to be a valid json.

Style:

previously, the `\"` trailing would be added in start of object, but this patch put it to end of object

Before:
```
stream << "\", \"number\":\""  << number;
stream << "\"...";
```

After:

```
stream << ", \"number\":\""  << number << "\"";
```

### Are these changes tested?

Yes

### Are there any user-facing changes?

Minor format change

* GitHub Issue: #44101

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: mwish <maplewish117@gmail.com>