Add support for yaml & json tmLanguage files

[gwennlbh]

VSCode allows tmLanguage files written in JSON instead of XML Plists, and I believe it would be useful to have that capability here, as a lot of people will start adding IDE support for their language with a VSCode extension, as it is the most popular code editor right now.^{this source dates back to 2019 but it's quite safe to assume it still is the case in 2022}

The change does not require any new dependency, as yaml support is built-in, and is a 3-line-change.

(Note that supporting YAML gives us JSON support for free, since the former is a superset of the latter)