fix handling of vscode configuration scopes

[akosyakov]

See #4947 (comment)

TODO

• update CHANGELOG from user perspective

[colin-grant-work]

@akosyakov, could you expand a little on the functionality that this issue is targeting? From the comment and the reference to the VSCode repo, it looks like the objective is to accurately reflect superset properties of scopes (User ⊃ Workspace ⊃ Folder), so anything valid in folder scope is valid in WS and User, and anything valid in WS is valid in User, but not vice versa. That needs to be reflected in how the schemas for each scope are updated and how the isValidInScope check works, correct? I think a lot of that work may already have been done, but I want to make sure I understand correctly what the desired functionality is.