Disambiguating multiple formatted files when writing to standard output

When using google-java-format to format multiple files and print their formatted results to standard-out, it's unclear how I'm supposed to disambiguate between the results in the output. For performance reasons, I am running google-java-format against my codebase in batches of 100 files at a time, and for various other reasons, formatting in-place is not preferred.

For example, running this:

```shell
java -jar $HOME/bin/google-java-format --aosp path/to/file1.java path/to/file2.java path/to/file3.java path/to/file4.java
```

results in output like this:

```shell
/* my file 1 */

public class File1 {
// ...
}
/* my file 2 */

public class File2 {
// ...
}
/* my file 3 */

public class File3 {
// ...
}
/* my file 4 */

public class File4 {
// ...
}
```

This example is kind of contrived, but the main point is that the end of file1.java and the start of file2.java, and so on, are not delimited in a clear way. What can I do here to clearly associate the output for each formatted file with its source path?

Comece com a invocação da CLI google-java-format mostrada na issue, concentrando-se na formatação de vários arquivos enviada para a saída padrão. Determine uma forma clara de associar cada resultado formatado ao seu caminho de origem e, em seguida, verifique o comportamento com o exemplo de quatro arquivos e uma entrada em lote equivalente.

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