[Blazor] Add mapping for .mjs files (#56316)

Newer emscripten produces dotnet.native.worker.mjs instead of .js
Context: dotnet/runtime#100334 (review)

Author: radekdoulik

src/Components/WebAssembly/Server/src/ComponentsWebAssemblyApplicationBuilderExtensions.cs

@@ -94,6 +94,7 @@ private static StaticFileOptions CreateStaticFilesOptions(IFileProvider webRootF
         AddMapping(contentTypeProvider, ".br", MediaTypeNames.Application.Octet);
         AddMapping(contentTypeProvider, ".dat", MediaTypeNames.Application.Octet);
         AddMapping(contentTypeProvider, ".blat", MediaTypeNames.Application.Octet);
+        AddMapping(contentTypeProvider, ".mjs", MediaTypeNames.Text.JavaScript);
 
         options.ContentTypeProvider = contentTypeProvider;