Enable DI container scope validation by default for Development environment in all ASP.NET Core 2.0 templates

Update all the ASP.NET Core 2.0 templates to turn on scope validation when in the development environment, e.g.:

public class Startup
{
    public Startup(IHostingEnvironment env)
    {
        HostingEnvironment = env;
    }

    public IHostingEnvironment HostingEnvironment { get; }

    public IServiceProvider ConfigureServices(IServiceCollection services)
    {
        // Set up container here...
        
        return services.BuildServiceProvider(validateScopes: HostingEnvironment.IsDevelopment());
    }

    public void Configure()
    {
        ...
    }
}

@glennc @davidfowl @pakrym @mlorbetske

[davidfowl]

Scope validation makes sure your dependency graph doesn’t have mismatched lifetimes (like depending on a scoped service from a singleton service). Read about “Captive dependencies” https://blog.ploeh.dk/2014/06/02/captive-dependency/

Simple injector also has a feature to detect this - https://simpleinjector.readthedocs.io/en/latest/LifestyleMismatches.html

[davidfowl]

We didn’t want the perf hit in production. Since you rarely change registrations at runtime (if ever) you’d catch most things at development time.