Update schema to equivalent of inlining "allOf"

[chrmarti]

We previously used a script to do this: https://github.com/microsoft/vscode/blob/main/extensions/configuration-editing/build/inline-allOf.ts

@aeschli mentioned a new schema feature to achieve the same while avoiding duplication: "unevaluatedProperties".

[chrmarti]

#167, microsoft/vscode#169857 and microsoft/vscode#171163.