[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.

L’issue non indica file, test o punti di ingresso. Inizia individuando la gestione esistente di jsonc nel repository della specifica e determina la superficie YAML prevista e i requisiti di compatibilità; i criteri di completamento non sono definiti nella proposta e richiedono un chiarimento da parte dei maintainer.

Scritto dal modello di indicizzazione a partire dal testo della issue.