QueryEndAtConstraint
A QueryEndAtConstraint is used to exclude documents from the end of a
result set returned by a Firestore query.
QueryEndAtConstraints are created by invoking {@link (endAt:1)} or
{@link (endBefore:1)} and can then be passed to {@link (query:1)} to create a new
query instance that also contains this QueryEndAtConstraint.
class QueryEndAtConstraint extends QueryConstraint {}
readonly type: "endBefore" | "endAt";