[proposal] Support yaml as well as jsonc

Any interest?

Background:
`jsonc`, aka "JSON with comments", while nicer than plain JSON, is still relatively new and doesn't have full ecosystem support yet. It also has some shortcomings shared with JSON, such as not accepting trailing commas in lists/objects (except on a [per-parser exception](https://github.com/microsoft/vscode/issues/102061) basis).

`yaml` can be limited to a JSON equivalent in terms of data structures it supports, and all (or at least most) of the issues with it were allayed in 1.2+ versions of the spec (such as `on` being parsed as `true` when not quoted). It also reduces the need for as many quotes, commas, open and close braces, and first-class supports comments.

Das Issue nennt keine Dateien, Tests oder Einstiegspunkte. Beginne damit, die vorhandene jsonc-Verarbeitung im Spec-Repository zu lokalisieren, und ermittle die vorgesehene YAML-Oberfläche und die Kompatibilitätsanforderungen; Abschlusskriterien sind im Vorschlag nicht definiert und müssen von den Maintainer:innen geklärt werden.

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