Counter for new files behaves differently for different file types

Positron Version:

Steps to reproduce the issue:

1. Open a new R script: Untitled-1. Don't save.
2. Open a new Python script: Untitled-2. The R script from Step 1 goes away. I think it shouldn't. Don't save.
3. Open a new Quarto document: Untitled-3. The Python script from Step 2 goes away. I think it shouldn't. Don't save.
4. Open a new Jupyter notebook: Untitled-1.ipynb. Counter resets! And the extension ipynb is visible in the editor. I think this is expected/good behaviour. Don't save.
5. Open a new R script: Untitled-4. Counter resuming from Step 3.
6. Open a new Python script: Untitled-5. And Untitled-4 is gone. Save this script.
7. Open a new Quarto document: Untitled-6.
8. Open a new Jupyter notebook: Untitled-2.ipynb. This is expected and nice.

https://github.com/posit-dev/positron/assets/5965649/244a715b-604b-443d-b4fc-3e05e750da3c

What did you expect to happen?

I expected:

• Counter to continue for the same file types
• New files not getting rid of previously created new files
  • Behaviour is good if I put any content in the file, even without saving, but I think it should be the same for no content new files as well
• The extension (.R, .py, etc.) to be shown for all files

Were there any error messages in the output or Developer Tools console?

None

Reproduce the sequence in Positron, covering unsaved empty R, Python, Quarto, and Jupyter files, and observe how names, extensions, and counters change. Trace the editor's new-file handling from that behavior; done means counters continue per file type, empty files remain open, and extensions are shown consistently.