Razor compiler warnings are not shown in dotnet build output

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Describe the bug

Razor compiler warnings (e.g., deprecation warnings) are not shown in the `dotnet build` output, even though they are triggered by Razor component usage.

This makes it easy to miss important warnings such as usage of obsolete APIs in `.razor` files.

### Expected Behavior

The warning should appear in the `dotnet build` output, just like C# warnings from `.cs` files.

### Actual behavior

The warning is not shown in the `dotnet build` output.

### Steps To Reproduce

Use the following Razor component:

```

Page not found

```

This produces the following compiler warning:

CS0618: Property 'Microsoft.AspNetCore.Components.Routing.Router.NotFound()' is obsolete: 'NotFound is deprecated. Use NotFoundPage instead.'

### Exceptions (if any)

_No response_

### .NET Version

10.0.200

### Anything else?

- The issue appears to affect Razor-generated code in general, not just this specific example.
- It seems that warnings emitted during Razor compilation or source generation are not consistently surfaced in the standard build output.
- This can lead to missed deprecations and other important diagnostics.

### Environment
**.NET SDK:**
Version: 10.0.200
Commit: 40cd698e5c
Workload version: 10.0.200-manifests.b7278506
MSBuild version: 18.3.0-release-26119-122+40cd698e5

### Impact
Developers may unknowingly ship code that relies on obsolete or problematic APIs because these warnings are either omitted from the build output or disregarded due to the `` annotation in the generated `.g.cs` files.

### Sample
Consider the App.razor file in the following attachement
[razorwarnings.zip](https://github.com/user-attachments/files/26304256/razorwarnings.zip)