[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.