Add File.java to forbidden APIs

This commit cuts over all of core (not quite all tests) to java.nio.Path
It also adds the file class to the core forbidden APIs to prevent its usage
Can we remove `throws IOException` and write:

```java
        try {
            if (!Files.exists(initialSettings.v2().pluginsFile())) {
                Files.createDirectories(initialSettings.v2().pluginsFile());
            }
        } catch (IOException e) {
            displayHelp("Unable to create plugins dir: " + initialSettings.v2().pluginsFile());
            System.exit(EXIT_CODE_ERROR);
        }
```