Summary

By manually constructing Dictionary indexes with `Expression` class in Linq, I can't access dictionary keys with MongoDB LinqV3.

MongoDB.Driver.Linq.ExpressionNotSupportedException: Expression not supported: it.Fields.Item["DynamicField1{_}{_}"].

MongoDB Driver: 2.19.0

How to Reproduce

```

public class SampleDocument

{

    public string Id { get; set; }

    [BsonDictionaryOptions(DictionaryRepresentation.Document)]
    public required IDictionary<string, object?> Fields { get; set; }

}

public class SampleRepository

{

    private readonly IMongoCollection<SampleDocument> _sampleDocumentCollection;

  public async ValueTask LoadSampleDocuments(
        CancellationToken cancellationToken = default)
    {
        var baseQuery = _sampleDocumentCollection
            .AsQueryable();

        if (true) {

            __            

            var searchableFields = new[] { "DynamicField1", "DynamicField2" };

            var parameter = Expression.Parameter(typeof(SampleDocument), "it");

            var dictType = typeof(IDictionary<string, object>);
            var dictionaryIndexer = dictType.GetProperty("Item")!;

            var expressions = searchableFields
                .Select(Expression.Equal(
                        Expression.MakeIndex(
                            Expression.Property(parameter, nameof(PolicyMemberStateDocument.Fields)),
                            dictionaryIndexer,
                            new List<Expression> { Expression.Constant(fieldPath) }),
                        Expression.Constant("SearchValue")))
                .ToList();
            var dynamicFilter = expressions[0];

            if (expressions.Count > 1)
            {
                foreach (var expression in expressions.GetRange(1, expressions.Count - 1))
               

            }

            var lambda = Expression.Lambda<Func<PolicyMemberStateDocument, bool>>(
                dynamicFilter,
                parameter);
            baseQuery = baseQuery.Where(lambda);

        }

       var result = await baseQuery.ToListAsync(cancellationToken);

}

```

Additional Background

Code in .NET repo that makes it `it.Fields.Item["DynamicField1"]` instead of `it.Fields["DynamicField1"]` : ExpressionStringBuilder.cs (microsoft.com)

I am building dynamic filtering for LinqV3 and encountered this issue for dynamic fields.

Stack trace:

MongoDB.Driver.Linq.ExpressionNotSupportedException: Expression not supported: it.Fields.Item["DynamicField1"].
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.ExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.BinaryExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, BinaryExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.ExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.BinaryExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, BinaryExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.ExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.TranslateUsingAggregationOperators(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.Translate(TranslationContext context, Expression expression, Boolean exprOk)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.TranslateLambda(TranslationContext context, LambdaExpression lambdaExpression, IBsonSerializer parameterSerializer, Boolean asRoot)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.WhereMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.OrderByMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.GroupByMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.SelectMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.WhereMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.OrderByMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.SkipMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.TakeMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToExecutableQueryTranslators.ExpressionToExecutableQueryTranslator.Translate[TDocument,TOutput](MongoQueryProvider`1 provider, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.MongoQuery`2.ToCursorAsync(CancellationToken cancellationToken)
   at MongoDB.Driver.IAsyncCursorSourceExtensions.ToListAsync[TDocument](IAsyncCursorSource`1 source, CancellationToken cancellationToken)