[BUG] Indexing a BicepDictionary as an output throws KeyNotFoundException

[eerhardt]

Library name and version

Azure.Provisioning

Describe the bug

In order to generate bicep like the following:

output connectionString string = 'Endpoint=${aiservices.properties.endpoints['Azure AI Model Inference API']}'

The C# code I wanted to write didn't work as expected.

Expected behavior

I expect the repro code to work and generate bicep with an indexer.

Actual behavior

Unhandled exception. System.Collections.Generic.KeyNotFoundException: The given key 'Azure AI Model Inference API' was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at Azure.Provisioning.BicepDictionary`1.get_Item(String key)
   at Program.<Main>$(String[] args) in D:\source\AspireApp6\AspireApp6.AppHost\Program.cs:line 10

Reproduction Steps

Run the following

using Azure.Provisioning;
using Azure.Provisioning.CognitiveServices;
using Azure.Provisioning.Expressions;

CognitiveServicesAccount ai = new(nameof(ai));

Infrastructure infra = new();
infra.Add(ai);

infra.Add(new ProvisioningOutput("connectionString", typeof(string))
{
    Value = BicepFunction.Interpolate($"Endpoint={ai.Properties.Endpoints["Azure AI Model Inference API"]}")
});

ProvisioningPlan plan = infra.Build();
string bicep = plan.Compile().First().Value;
Console.WriteLine(bicep);

Environment

cc @tg-msft @m-nash

[jsquire]

//cc: @m-nash, @tg-msft