Collapse/Remove namespace/header info at the top of C# code display

[michael-hawker]

We should either have a collapsible region at the top of the C# code display for samples that hides the license info and namespaces to better focus on the code for the specific sample (or remove it entirely).

We may also want to hide the page constructor if it's completely default and just calling InitializeComponent.

[Arlodotexe]

Including the namespaces will be almost necessary for samples, so we probably shouldn't remove them completely.

Things that may help:

• Raising the severity for unused namespaces at the top of sample pages
• Sample tabs for compilation-conditional code that swaps between UWP and WinAppSDK