Folder structure: Controls, Design, Accessibility, Fundamentals

This app used to be named "Control Gallery", but has evolved to encompass many more things. The current folder structure - and some file names - are still, inappropriately, centered on "Controls".

• 📂 ControlPages > Accessibility, DesignGuidance, Fundamentals
• File names like "ControlData<Schema>.json" and their content

sub of #1614

Suggested

• AppControls
• AppPages
• Samples
  • SampleCode (level "A")
    • Accessibility (level "B")
    • Design
      • Iconography
      • Geometry
      • Typography
    • Fundamentals
      • Binding
      • Templates
      • XamlResources
      • XamlStyles
    • XamlControls
      • 📄 (many txt files)
  • SampleData
    • 📄 (files like AccessibilityData.json, ControlData.json, DesignData, IconData.json, ...)
  • SamplePages (level "A") (not to be mistaken with the current folder with the same name!)
    • Accessibility
    • Design
      • Iconography
      • Geometry
      • Typography
    • Fundamentals
      • Binding
      • Templates
      • XamlResources
      • XamlStyles
    • XamlControls
      • 📄 (many xaml files)

Also

• use names📁 "AppControls" and "XamlControls" to prevent any ambiguity.
• looks like 📁 "SamplePages" isn't used? if not, let's remove it.
• I want to split ControlInfoData into separate files and code.
• ... then must update ItemPage.xaml.cs and ControlInfoData.cs for ControlInfoDataItem ❗
• ... a filename like 📄 "...InfoData" is redundant. Info == Data.

Start by inventorying the current ControlPages, SamplePages, ControlInfoData files, and related names in ItemPage.xaml.cs and ControlInfoData.cs. Align the folders and filenames with the suggested AppControls, XamlControls, SampleCode, SampleData, and SamplePages structure, remove SamplePages if unused, and update the referenced data and code consistently.