Remote native debugging Playground with web debugging doesn't work anymore

[kmelmon]

We added some support for remote debugging the Playground app, see:
https://github.com/microsoft/react-native-windows/wiki/VS-Remote-Debugging

However this technique doesn't work anymore. I debugged this and found two issues:

1. The privateNetworkClientServer capability isn't turned on in Package.appxmanifest
2. The client code is failing to connect due to using localhost:8081. It looks like we're missing the plumbing code that was originally added to HostingPane, which is no longer being used in Playground.

We should find a way to re-enable this. We should also think about how to enable remote debugging for CLI apps when we fix this - ideally whatever we do would also work for template apps.

[kmelmon]

See this PR which originally fixed Playground:
#3535

[kmelmon]

Also, update this wiki page when this is fixed:
https://github.com/microsoft/react-native-windows/wiki/VS-Remote-Debugging

[nasadigital]

I can pick this up.
As @kmelmon mentioned if privateNetworkClientServer is enabled and I add an option to specify the hostname and/or port (similar to how it's done in #5062), remote debugging works for me similarly to how it's outlined in the wiki.
This approach should work with template apps as well.

[nasadigital]

The PR only fixes remote debugging in the Playground app and doesn't address remote debugging with CLI or with Visual Studio for the template apps, so I'm reopening the issue.