AddASetting.md does not appear to be up-to-date

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### Description of the new feature

I am trying to implement issue #6820 and am using AddASetting.md to do so. However, when trying to follow the instructions I notice that the instructions don't seem to match existing elements. The instructions say to declare the setting in Profile.h (or in my case, GlobalAppSettings.h), but the settings seem to be defined in Profile.idl instead, and the lines of code the instructions say to add to Profile.idl don't seem to be present for any other settings in that file.

I would like this implementation to not simply work but follow the design practices of the existing window settings. Is this guide out-of-date, and if it isn't why is the guide's implementation so different from the existing implementations?

### Proposed technical implementation details

_No response_

Start by reading AddASetting.md and compare its instructions with the existing definitions in Profile.idl and the references to Profile.h and GlobalAppSettings.h. Use the window settings related to issue #6820 as the comparison point. Done means the guide accurately reflects the current implementation and design practices, or clearly explains why the documented process differs.

Written by the indexing model from the issue text.