Template/Repo: Use File Scoped Namespaces

[michael-hawker]

I noticed we're using the extra indent in the namespace, since we're using newer C# language level, we can just condense this using the flat namespaces (they're really nice).

Labs-Windows/template/lab/src/ProjectTemplate.cs

Lines 29 to 34 in e6389b0

	namespace CommunityToolkit.Labs.WinUI
	{
	public class ProjectTemplate
	{
	}
	}

Would become:

namespace CommunityToolkit.Labs.WinUI;
 
public class ProjectTemplate 
{ 
} 

We'd want to update all the files in the template for library, samples, tests. And possible anywhere else in the repo, like the main sample app.

Along with #144, should help keep things pretty lean and clean for getting started with an experiment.

[mrlacey]

As I was confused by the issue title and assumed this was going to be something else. This feature is called "File Scoped Namespaces" https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-10.0/file-scoped-namespaces 😉