Add support to hook into MVC and WebApi DI frameworks

[twsouthwick]

This change adds support for integrating the host's dependency injection into the ASP.NET Framework entrypoints. This is done by adding a source generator that will inject the appropriate hooks so we don't have to take a dependency on the actual frameworks.

A user can consume this as simply as:

builder.AddSystemWebDependencyInjection();

and it will be hooked up to all the DI frameworks (and it's extensible for others to add more if needed with the interface IDependencyRegistrar)

This also adds the following:

• A simple way to get request scoped dependencies from HttpContext.GetRequestServices() that will work on framework or core
• An analyzer to ensure people don't try to use the IServiceProvider from HttpContext which does absolutely nothing and can't be overridden or extended.

[Copilot]

Pull Request Overview

This PR adds dependency injection integration for ASP.NET Framework applications by hooking into MVC and Web API DI frameworks through source generation. Users can now enable DI with a single builder.AddSystemWebDependencyInjection() call.

Key Changes:

• Source generator that conditionally includes MVC/WebAPI DI hooks without hard dependencies
• Extension methods to retrieve request-scoped services consistently across Framework and Core
• Analyzer to prevent usage of the non-functional HttpContext.GetService method

Reviewed Changes

Copilot reviewed 24 out of 25 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Microsoft.AspNetCore.SystemWebAdapters/HttpContextRequestServicesExtensions.cs	New extension methods for accessing request services across platforms
src/Microsoft.AspNetCore.SystemWebAdapters.FrameworkServices/WebObjectActivatorExtensions.cs	Refactored to use new IDependencyRegistrar pattern for multiple DI frameworks
src/Microsoft.AspNetCore.SystemWebAdapters.Analyzers.CSharp/FrameworkDependencyInjectionGenerator.cs	Source generator that creates DI registration code based on referenced assemblies
src/Microsoft.AspNetCore.SystemWebAdapters.Analyzers/HttpContextDependencyAnalyzer.cs	Analyzer preventing use of non-functional HttpContext.GetService
samples/*/Global.asax.cs	Updated to use new AddSystemWebDependencyInjection() method

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[CZEMacLeod]

Would it be possible to use the new extension members format and make this a property called RequestServices to more closely align with the new Core api?
I've tested it briefly and it does seem to compile and work, but VS2022 IDE is not happy - seemed okay in VS2026 though.

Maybe this will be more possible when the net 10 sdk is released....

[twsouthwick]

I would like that, but I don't think we currently have anything that would require using something greater than 7.3 on framework apps, and I don't really want to start now.

If we've used things that require using > c# 7.3, then I may be more ok with it.