Match MR tree view order to list and file order

What does this MR do and why?

For #562606 (closed)

Fixes the sort functionality of the MR Changes tab while in Tree view mode to match the order in list view and the actual returned order of the diff files from the back end.

Screenshots or screen recordings

The only change is in the tree view of the file browser.

List view is unchanged.

Before	After

How to set up and validate locally

(More complete reproduction steps can be found in the linked issue)

1. Create an MR that includes files in a sub-directory and in a sub-sub-directory whose first level matches the prefix of the other sub-directory.
   • For example example-dir/file.file and example/thing/file.file (they share the example prefix).
2. Visit the changes tab of your MR
3. Ensure the file browser is open and using Tree view mode
   • Switching to List view mode - as well as confirming against the diff file order on the right side - will confirm the order is the same.

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