[BUG] Bicep Expressions don't work in Interpolated strings

[eerhardt]

Library name and version

Azure.Provisioning

Describe the bug

When trying to use an expression in an interpolated string, the expression doesn't get interpolated correctly.

Expected behavior

The output bicep should look like:

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

Actual behavior

output connectionString string = 'Endpoint=ai.properties.endpoints[\'Azure AI Model Inference API\']'

Reproduction Steps

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

CognitiveServicesAccount ai = new(nameof(ai));

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

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

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

NOTE: If I cast the IndexExpression to a BicepValue<string> explicitly, then it does produce the right bicep.

var inferenceEndpoint = (BicepValue<string>)new IndexExpression(
    (BicepExpression)ai.Properties.Endpoints!,
    "Azure AI Model Inference API");
infra.Add(new ProvisioningOutput("connectionString", typeof(string))
{
    Value = BicepFunction.Interpolate($"Endpoint={inferenceEndpoint}")
});

Environment

cc @tg-msft @m-nash

[jsquire]

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