Update tree view to sort folders with submodules

This updates the project tree view to show submodules alphabetically sorted with folders, rather than putting all submodules under the files

Before After

Whereas before we used to sort in the fashion (with each section subsorted alphabetically):

• folders
• files
• submodules

We now sort (with each section subsorted alphabetically):

• folders & submodules
• files

Checklist

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

Closes #19727 (closed)