Plugin: exclude existing fields from autocomplete unless alias is used

I think autocompletion should be aware of current queryString, because you then get hit for fields what are currently in query.

Here: https://github.com/graphql/graphql-language-service/blob/master/packages/interface/src/getAutocompleteSuggestions.js#L86

we get suggestion for everything available in schema and query string is completely ignored. https://i.imgur.com/heB9sRS.gif