This is a list of potential enhancements to the ToolProvider API.

1. Provide 1 or 2 static methods to expand @-files. These would be similar to the public methods on the internal `CommandLine` class, which now exists in 3 separate places. If there was only one method, it might be

   public static List<String> expandArgumentFiles(List<String> args)

If there was an additional method, it might be to support an environment variable, as in

   public static List<String> expandArgumentFiles(String envVar, List<String> args)

For reference, see
https://github.com/openjdk/jdk/blob/master/src/jdk.compiler/share/classes/com/sun/tools/javac/main/CommandLine.java

Internally, this might be implemented by adding `CommandLine` as an internal nested class of ToolProvider, with just a public static method to invoke it.