docs: Improved DI documentation (#2407)

docs/guides/dependency_injection/samples/provider.cs

@@ -0,0 +1,26 @@
+public class UtilizingProvider
+{
+    private readonly IServiceProvider _provider;
+    private readonly AnyService _service;
+
+    // This service is allowed to be null because it is only populated if the service is actually available in the provider.
+    private readonly AnyOtherService? _otherService;
+
+    // This constructor injects only the service provider,
+    // and uses it to populate the other dependencies.
+    public UtilizingProvider(IServiceProvider provider)
+    {
+        _provider = provider;
+        _service = provider.GetRequiredService<AnyService>();
+        _otherService = provider.GetService<AnyOtherService>();
+    }
+
+    // This constructor injects the service provider, and AnyService,
+    // making sure that AnyService is not null without having to call GetRequiredService
+    public UtilizingProvider(IServiceProvider provider, AnyService service)
+    {
+        _provider = provider;
+        _service = service;
+        _otherService = provider.GetService<AnyOtherService>();
+    }
+}