WebApplicationBuilder throws DirectoryNotFoundException when wwwroot is empty but has links

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Describe the bug

The issue occurs if the following happen:
* An Asp.Net Core hosted blazor application is used
* A razor class library is referenced by the client project
* The wwwroot project of the razor class library is empty except for `` items

Then the application throws `System.IO.DirectoryNotFoundException: 'C:\Git\Repro\Repro\RCL\wwwroot\'` at startup

### Expected Behavior

No exception should be thrown at startup

### Steps To Reproduce

https://github.com/TomGathercole/EmptyWwwrootRepro

### Exceptions (if any)

System.IO.DirectoryNotFoundException
HResult=0x80070003
Message=C:\Git\Repro\Repro\RCL\wwwroot\
Source=Microsoft.Extensions.FileProviders.Physical
StackTrace:
at Microsoft.Extensions.FileProviders.PhysicalFileProvider..ctor(String root, ExclusionFilters filters)
at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.<>c.b__1_0(String contentRoot)
at Microsoft.AspNetCore.StaticWebAssets.ManifestStaticWebAssetFileProvider..ctor(StaticWebAssetManifest manifest, Func`2 fileProviderFactory)
at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.UseStaticWebAssetsCore(IWebHostEnvironment environment, Stream manifest)
at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.UseStaticWebAssets(IWebHostEnvironment environment, IConfiguration configuration)
at Microsoft.AspNetCore.Hosting.BootstrapHostBuilder.RunDefaultCallbacks()
at Microsoft.AspNetCore.Builder.WebApplicationBuilder..ctor(WebApplicationOptions options, Action`1 configureDefaults)
at Microsoft.AspNetCore.Builder.WebApplication.CreateBuilder(String[] args)
at Repro.Program.Main(String[] args) in C:\Git\Repro\Repro\Server\Program.cs:line 9

### .NET Version

7.0.306

### Anything else?

It looks like `C:\Git\Repro\Repro.RCL\wwwroot\` is included under `ContentRoots` in the `Repro.RCL.staticwebassets.runtime.json` file, even if the file does not exist. I suppose that this path should not be included if it does not exist, or StaticWebAssetsLoader shouldn't throw if it is missing