Currently Equals is limited to struct, IComparable which excludes strings

public SearchDefinition<TDocument> Equals<TField>(
    FieldDefinition<TDocument, TField> path,
    TField value,
    SearchScoreDefinition<TDocument> score = null)
    where TField : struct, IComparable<TField> =>
        new EqualsSearchDefinition<TDocument, TField>(path, value, score);

Since Atlas Search now supports equals operator on token types, an overload with the string type would be useful.

Also, overloads for IEnumerable<TField> on equals would also be nice to have since equals also supports array fields, so we can do this

Builders<A>.Search.Equals(x => x.IntArray, 1)
Builders<A>.Search.Equals(x => x.StringArray, "")