HttpDependencyMetadataResolver class for the custom downstream dependency metadata resolution

[rainsxng]

As per following API proposal, this PR exposes the DownstreamDependencyMetadataManager class with the new name that allows you to configure the downstream dependency metadata resolution and brings more flexibility into the flow

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR refactors the downstream dependency metadata resolution system by introducing a new public API HttpDependencyMetadataResolver to replace the internal IDownstreamDependencyMetadataManager interface. The changes expose the dependency metadata resolution functionality with improved naming and flexibility.

• Renames internal DownstreamDependencyMetadataManager to public HttpDependencyMetadataResolver as an abstract class
• Adds DefaultHttpDependencyMetadataResolver as the default implementation
• Updates registration methods to use TryAddEnumerable for proper DI behavior with multiple metadata instances

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
HttpDependencyMetadataResolver.cs	Converts internal sealed class to public abstract class with documentation and removes obsolete HttpWebRequest support
DefaultHttpDependencyMetadataResolver.cs	New sealed class providing default implementation of the resolver
HttpDiagnosticsServiceCollectionExtensions.cs	Updates registration to use TryAddEnumerable and adds new AddStandardHttpDependencyMetadataResolver method
HttpRequestReader.cs	Updates field and parameter names to use new resolver type
IDownstreamDependencyMetadataManager.cs	Marks internal interface as obsolete
DownstreamDependencyMetadataManagerTests.cs	Updates test class to use new resolver type and namespace