[Blazor] AuthorizeViewCore should expose AuthorizationResult to NotAuthorized template

`AuthorizeViewCore` currently only exposes an `AuthenticationState` context to the `NotAuthorized` render fragment. It does not provide access to the full `AuthorizationResult`, including `AuthorizationFailureReason` messages set by custom authorization handlers.

### Problem

When implementing custom authorization handlers that use `context.Fail(new AuthorizationFailureReason(...))` to provide detailed failure messages, there is no supported way to surface these messages in the `NotAuthorized` render fragment.

The current implementation in `AuthorizeViewCore.IsAuthorizedAsync()` discards the full authorization result:

```csharp
var result = await AuthorizationService.AuthorizeAsync(user, Resource, policy!);
return result.Succeeded; // Only boolean is returned, AuthorizationResult is lost
```

### Proposed Solution

Introduce a new `Forbidden` render fragment that handles the "authenticated but not authorized" (403) case separately from `NotAuthorized`. This new fragment would have a context type that includes `AuthorizationResult` and failure reasons, enabling developers to display detailed error messages. This approach mirrors HTTP semantics (401 vs 403) and keeps `NotAuthorized` backward-compatible.

### Alternatives Considered

- **Add a new property to expose `AuthorizationResult`** - Not ideal as it can't be easily consumed within the render fragment context.
- **Introduce a new context type extending `AuthenticationState`** - Same usability concerns; doesn't integrate naturally with the existing templating model.
- **Use a cascading parameter** - Requires creating an additional wrapper component to consume the result, adding unnecessary complexity.

### Desired Behavior

Allow developers to display custom error messages (e.g., "Missing permission: project.read") instead of generic "Access Denied" text when authorization fails.

### Related

Extracted from: #65007