Restructure samples

[marcelwgn]

This is a draft to garner feedback before we fully convert one example to so AI can convert the rest

We are introducing a new SampleCodePath property on ControlExample that loads both XAML and C# code snippets from a single file using a simple section-based format:

 --- xaml
 <Button Content="Click me" />
 --- c#
 private void OnClick() { }

Sections are identified by --- followed by the type (xaml or c#). They can appear in any order, and either may be omitted.

Folder restructuring:

• Moved ButtonPage + its sample code into Samples/Button/ to have a per-control folder pattern
• Moved Data, SampleHelpers, and SamplePages from Samples/ into a new SampleSupport/ root folder to separate support files from actual sample pages

Namespaces are unchanged - only physical file locations and MSBuild/runtime path references were updated.

Future direction: The --- type marker format is designed to be extensible. In a future change, metadata like title and description could also be inlined in the same file (e.g. --- title, --- description), allowing a single file to fully describe a control example (except the code needed for setup of course)

[niels9001]

Nit: nameof() instead of string.

[marcelwgn]

/azp run