Consider replacing `FileOutputStream` with `Files.newOutputStream`

Since Java 7 two methods are available to open new files:

- [`FileOutputStream#new`](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/io/FileOutputStream.html),
- [`Files#newOutputStream`](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/nio/file/Files.html#newOutputStream(java.nio.file.Path,java.nio.file.OpenOption...)).

While they mostly perform the same OS operations, there is a significant difference between the two on Windows: the IO method opens the file **without** the `FILE_SHARE_DELETE` option, whereas the NIO method adds the `FILE_SHARE_DELETE` option (cf. [this SO question](https://stackoverflow.com/q/63584311/11748454)).

Since log files on UNIX can already be deleted without stopping the application, this change would allow an alignment between the behavior of Log4j on Windows and UNIX.

I discussed this with @garydgregory on Slack.