new ApplicationBuilder(ApplicationBuilder builder) should copy the Properties dictionary

[tuespetre]

As I was trying to use Map and set a custom service provider ApplicationServices within the branch, I found that setting ApplicationServices on the branched application was also setting it on the application builder that was branched from, due to both application builders sharing the same properties dictionary. This feels counter-intuitive -- I expected that a new IApplicationBuilder in a new branch would have its own properties.

[muratg]

@tuespetre Interested in sending a PR? If you do, please use https://github.com/aspnet/Common/blob/dev/shared/Microsoft.Extensions.CopyOnWriteDictionary.Sources/CopyOnWriteDictionary.cs instead of doing a clone on the constructor.