json.Encoder and json.Marshal implicitly use HTMLEscape to convert
>, <, &, with \u003c, \u003e, \u0026. This behavior carries over
to yq, where chars will be escaped when outputting json but not when
outputting yaml.
This changeset disables this behavior via encoder.SetEscapeHTML(false).
Unfortunately there is no equivalent option for json.Marshal, so its
single usage has been replaced with an encoder (with escaping disabled).