docs(dotnet): fix Blazor WebAssembly example (#15731)

## DESCRIBE YOUR PR
Reported through User Feedback:

- method `UseSentry` on `WebAssemblyHostBuilder` not found
- method `AddSentry` on `ILoggingBuilder` not found

The user's `.csproj` either does not include
`<ImplicitUsings>enable</ImplicitUsings>` (from newer .NET SDK
templates), or has explicitly disabled the implicit usings from the
`Microsoft.NET.Sdk.BlazorWebAssembly` Project-SDK
(`<ImplicitUsings>disable</ImplicitUsings>`).

In cases where project code has global using declarations for these
namespaces already (implicitly or explicitly), in worst case, these
using declarations are redundant.

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## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [ ] Checked Vercel preview for correctness, including links
- [ ] PR was reviewed and approved by any necessary SMEs (subject matter
experts)
- [ ] PR was reviewed and approved by a member of the [Sentry docs
team](https://github.com/orgs/getsentry/teams/docs)

Co-authored-by: James Crosswell <[email protected]>

Author: Flash0ver

docs/platforms/dotnet/guides/blazor-webassembly/index.mdx

@@ -29,6 +29,9 @@ Sentry integration with Blazor WebAssembly is done by calling `.UseSentry()` and
 
 
 ```csharp
+using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
+using Microsoft.Extensions.Logging;
+
 var builder = WebAssemblyHostBuilder.CreateDefault(args);
 builder.UseSentry(options =>
 {