Files.newOutputStream throws if file is a symlink to a non-existing target.

For simplicity, here is what I do in bash:

```
$ ls symlink-target
> ls: symlink-target: No such file or directory
$ ln -s symlink-target symlink-source
$ echo hello > symlink-source
$ cat symlink-target
> hello
```

Jimfs would throw the following (version: `1.2`)

```
java.nio.file.FileSystemException: symlink-source: not a regular file
at com.google.common.jimfs.FileSystemView.getOrCreateRegularFileWithWriteLock(FileSystemView.java:336)
at com.google.common.jimfs.FileSystemView.getOrCreateRegularFile(FileSystemView.java:298)
at com.google.common.jimfs.JimfsFileSystemProvider.newOutputStream(JimfsFileSystemProvider.java:201)
at java.base/java.nio.file.Files.newOutputStream(Files.java:228)
```

The code would work fine if I were to use `Filesystems.getDefault()`, and as show at the top, this would also work in the CLI.