Allow ungrouped settings in the Settings editor extensions ToC

[rzhao271]

See #126089 (comment)

An idea is that if the category title is the same as the main extension title, then the settings should just be in a group under the main extension heading itself in the Settings editor.

[rzhao271]

Verification steps:

1. Clone, build, and run the following extension https://github.com/rzhao271/settings-editor-tocsort.
2. Open the Settings editor and look at the "Extensions" section of the table of contents (extensions ToC).

What we want:

1. There should be an entry called "Z extension" near the bottom of the list of extensions.
2. That extension should have three categories in the order A, B, and C.
3. One should be able to click on the "Z extension" entry itself. That action results in the Settings editor focusing on the heading "Z extension", and there should be settings J, K, and L right under that heading. After those settings, there should be a subheading for the A category.

Also see #137257 as that issue has very similar verification steps.