Fix executable arguments showing raw manifest expressions in dashboard

[Copilot]

After upgrading to Aspire 9.2, executable resources started showing raw manifest expressions like {{- portForServing "exe" -}} instead of resolved values in the dashboard's Source column when using endpoint references in arguments.

The issue was in the ExpressionResolver class which only handled endpoint expressions when the source was a container (sourceIsContainer = true). For executable resources, endpoint expressions would fall through to the generic IValueProvider case and return unresolved template expressions.

Before the fix:

var app = builder.AddExecutable("exe", "pwsh.exe", ".")
    .WithHttpEndpoint();
var endpoint = app.GetEndpoint("http");

app.WithArgs("-port")
    .WithArgs(x => x.Args.Add(endpoint.Property(EndpointProperty.TargetPort)));
// Dashboard would show: {{- portForServing "exe" -}}

After the fix:

// Same code now shows the resolved port number: 12345

The fix removes the when sourceIsContainer condition from the endpoint expression handlers in ExpressionResolver.ResolveInternalAsync(), allowing endpoint expressions to be properly resolved for both container and executable sources. The existing EvalEndpointAsync method already contains the correct logic to handle different communication scenarios (container-to-container, executable-to-container, etc.).

Fixes #9047.

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