private static FileSystem getOrCreateJarFS(URI jarURI) {
		Map<String, String> env = new HashMap<>();
		try {
			return FileSystems.getFileSystem(jarURI);
		}
		catch (FileSystemNotFoundException e) {
			try {
				return FileSystems.newFileSystem(jarURI, env);
			}
			catch (IOException e1) {
				Msg.debug(FileUtilities.class, "Unexepecedly could not create jar filesystem");
				return null;
			}
		}
	}
Return the relative path string of one resource file in another. If no path can be 
constructed or the files are the same, then null is returned.

Note: unlike {@link #relativizePath(File, File)}, this function does not resolve symbolic 
links.

<P>For example, given, in this order, two files with these paths
 <code>/a/b</code> and <code>/a/b/c</code>, this method will return 'c'.

@param f1 the parent resource file
@param f2 the child resource file
@return the relative path of {@code f2} in {@code f1}; null if f1 is not a parent of f2
Ghidra/Framework/Utility/src/main/java/utilities/util/FileUtilities.java