Allow serving of unknown files (#299)

By default, we only serve files with known MIME types, but that is an issue when dotnet library tests consume over a hundred different file extensions in their tests

src/Microsoft.DotNet.XHarness.CLI/Commands/WASM/Browser/WasmTestWebServerStartup.cs

@@ -31,7 +31,8 @@ public void Configure(IApplicationBuilder app)
             app.UseStaticFiles(new StaticFileOptions
             {
                 FileProvider = new PhysicalFileProvider(s_hostingEnvironment.ContentRootPath),
-                ContentTypeProvider = provider
+                ContentTypeProvider = provider,
+                ServeUnknownFileTypes = true
             });
         }
     }