support single file embedded assemblies

runtime compilation in .net 6 app published as a single file (`true`) works only with extraction to filesystem (`true`).

without extraction, it throws:
```
System.ArgumentException: The value cannot be an empty string. (Parameter 'path')
at System.ArgumentException.ThrowNullOrEmptyException(String argument, String paramName)
at System.IO.Strategies.FileStreamHelpers.ValidateArguments(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, Int64 preallocationSize)
at System.IO.File.OpenRead(String path)
at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RazorReferenceManager.CreateMetadataReference(String path)
at System.Linq.Enumerable.SelectListIterator`2.ToList()
at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RazorReferenceManager.GetCompilationReferences()
at System.Threading.LazyInitializer.EnsureInitializedCore[T](T& target, Boolean& initialized, Object& syncLock, Func`1 valueFactory)
at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RazorReferenceManager.get_CompilationReferences()
at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.LazyMetadataReferenceFeature.get_References()
at Microsoft.CodeAnalysis.Razor.CompilationTagHelperFeature.GetDescriptors()
at Microsoft.AspNetCore.Razor.Language.DefaultRazorTagHelperBinderPhase.ExecuteCore(RazorCodeDocument codeDocument)
at Microsoft.AspNetCore.Razor.Language.RazorEnginePhaseBase.Execute(RazorCodeDocument codeDocument)
at Microsoft.AspNetCore.Razor.Language.DefaultRazorEngine.Process(RazorCodeDocument document)
at Microsoft.AspNetCore.Razor.Language.DefaultRazorProjectEngine.ProcessCore(RazorCodeDocument codeDocument)
at Microsoft.AspNetCore.Razor.Language.RazorProjectEngine.Process(RazorProjectItem projectItem)
at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RuntimeViewCompiler.CompileAndEmit(String relativePath)
at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RuntimeViewCompiler.OnCacheMiss(String normalizedPath)
--- End of stack trace from previous location ---
```

https://learn.microsoft.com/en-us/dotnet/core/deploying/single-file/overview?tabs=cli#api-incompatibility

if file-on-disk requirement is the only thing limiting user to access razor runtime compilation in `PublishSingleFile` apps, please consider adding support of in-memory assemblies without going through file i/o.

aside: in .net 7, this problem becomes real with `true`. there is no workaround as `IncludeAllContentForSelfExtract` because nativeaot does not use apphost.