Jardesc XML output order is non-deterministic

Forgive me if this is in the wrong eclipse project. This is my best guess.

When creating a jardesc via the jar export dialog, the resulting jardesc file includes a (potentially large) number of `javaElement` and `file` tags. If I modify a jardesc file and save the result, it will often save the elements in a completely different order. This of course doesn't affect the actual creation of a jar file, but it makes it nearly impossible to tell what changed by looking at a diff.

If the elements could be output in some deterministic order (perhaps alphabetized?) then it would make it much easier for me to review and understand changes in git diffs.

Start by tracing how the jar export dialog loads and saves jardesc XML, focusing on the serialization of javaElement and file tags. Confirm the current ordering behavior with a jardesc containing multiple elements, then verify that saving it repeatedly produces deterministic ordering and stable diffs.

Written by the indexing model from the issue text.