We replaced previously used aggregation stage snippets with Stage/Query/Aggregation API completions. There are no more comment blocks for snippets. The MQL suggestion follows the same suggestion logic that Compass does: the `$match` stage uses the Query autocomplete, whereas for everything else we will use an unspecific set of various Aggregation expressions, BSON types, etc. We will not try to autocomplete generated fields, e.g. fields that are created within other fields of the pipeline. That is a hard problem to solve as with the freedom of a playground someone can be composing aggregations in many different ways, breaking down pipelines and stages into chunks that get only combined together at runtime.