Fixed issues with caching in the wrong slot

[davidfowl]

• When using ValidateOnBuild we build the callsite for each ServiceDescriptor but using the wrong slot. This didn't matter before but it breaks service overrides.
• Run the spec tests with ValidateOnBuild set to true when it doesn't throw.

var services = new ServiceCollection();

services.AddTransient<IFoo, Foo1>();
services.AddTransient<IFoo, Foo2>();

var sp = services.BuildServiceProvider(new ServiceProviderOptions
{
    ValidateOnBuild = true
});

Console.WriteLine(sp.GetRequiredService<IFoo>());

interface IFoo { }
class Foo1 : IFoo { }
class Foo2 : IFoo { }

This should print Foo2, it was printing Foo1 when ValidateOnBuild was true.

Currently blocking dotnet/aspnetcore#32315

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Issue Details

---

• When using ValidateOnBuild we build the callsite for each ServiceDescriptor but using the wrong slot. This didn't matter before but it breaks service overrides.
• Run the spec tests with ValidateOnBuild set to true when it doesn't throw.

Currently blocking dotnet/aspnetcore#32315

Author:	davidfowl
Assignees:	-
Labels:	area-Extensions-DependencyInjection
Milestone:	-