Added AvaloniaLocation.GetRequiredService.

Using the pattern from elsewhere e.g. https://docs.microsoft.com/en-us/dotnet/api/microsoft.extensions.dependencyinjection.serviceproviderserviceextensions.getrequiredservice?view=dotnet-plat-ext-6.0

src/Avalonia.Base/AvaloniaLocator.cs

@@ -125,6 +125,16 @@ namespace Avalonia
         {
             return (T?) resolver.GetService(typeof (T));
         }
+
+        public static object GetRequiredService(this IAvaloniaDependencyResolver resolver, Type t)
+        {
+            return resolver.GetService(t) ?? throw new InvalidOperationException($"Unable to locate '{t}'.");
+        }
+
+        public static T GetRequiredService<T>(this IAvaloniaDependencyResolver resolver)
+        {
+            return (T?)resolver.GetService(typeof(T)) ?? throw new InvalidOperationException($"Unable to locate '{typeof(T)}'.");
+        }
     }
 }
 

src/Avalonia.Controls/SystemDialog.cs

@@ -66,8 +66,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            var service = AvaloniaLocator.Current.GetService<ISystemDialogImpl>() ??
+            var service = AvaloniaLocator.Current.GetRequiredService<ISystemDialogImpl>();
-                throw new InvalidOperationException("Unable to locate ISystemDialogImpl.");
             return (await service.ShowFileDialogAsync(this, parent) ??
              Array.Empty<string>()).FirstOrDefault();
         }
@@ -95,8 +94,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            var service = AvaloniaLocator.Current.GetService<ISystemDialogImpl>() ??
+            var service = AvaloniaLocator.Current.GetRequiredService<ISystemDialogImpl>();
-                throw new InvalidOperationException("Unable to locate ISystemDialogImpl.");
             return service.ShowFileDialogAsync(this, parent);
         }
     }
@@ -125,8 +123,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            var service = AvaloniaLocator.Current.GetService<ISystemDialogImpl>() ??
+            var service = AvaloniaLocator.Current.GetRequiredService<ISystemDialogImpl>();
-                throw new InvalidOperationException("Unable to locate ISystemDialogImpl.");
             return service.ShowFolderDialogAsync(this, parent);
         }
     }