Consider exposing the application url using IWebAssemblyHostEnvironment

[pranavkm]

Application developers that need to resolve a resource from their app in Program.MainAsync have to build the IServiceCollection and resolve the NavigationManager from DI. We usually tell users not to build the service container. It would be much more convenient if the interface exposed the URI. In tandem with #19900, this would make doing things at startup much more reasonable. We could even consider removing the AddBaseAddressHttpClient extension method if this were available:

public sealed class WebAssemblyHostBuilder
{
       ///  <summary>Gets the <see cref="IWebAssemblyHostEnvironment" />.
+    public IWebAssemblyHostEnvironment HostEnvironment { get; }
}

public interface IWebAssemblyHostEnvironment
{
+    /// <summary> Gets the application base address</summary>
+    public Uri BaseAddress { get; }
}

// Blazor-wasm Template
public static async Task Main(...)
{
-  builder.Services.AddBaseAddressHttpClient();
+  builder.Services.AddSingleton(new HttpClient { BaseAddress = builder.HostEnvironment.BaseAddress });
}

The last bit might also play better with users having to configure a custom HttpMessageHandler on the HttpClient instance.

[Tratcher]

Where would this get populated from?

[pranavkm]

This is the Blazor Wasm specific host environment. The app is hosted at where the browser is pointing at, and we know this value from the browser.

[captainsafia]

Closed via #20019.