Add support for StorageFile.GetThumbnailAsync

[jamesmcroft]

What would you like to be added:

Bring support for the StorageFile.GetThumbnailAsync method across supported platforms.

Why is this needed:

This would allow developers to render the generated thumbnail image in their applications.

For which Platform:

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• macOS
• Skia
  • WPF
  • GTK (Linux)
  • Tizen
• Windows
• Build tasks
• Solution Templates

Anything else we need to know?

Would be nice to get as many platforms as possible but understand that this might not be achievable.

I've not completely explored this before, but I know that Android has limited MediaStore APIs for thumbnails for images and videos (unsure if it extends to any file format).

[jeromelaban]

Note for contributors

Implementing this would require a dependency on SkiaSharp (or any other image decoding library), most likely through an API extension integration, so that SkiaSharp may not come weighing down on apps that don't use that feature, or to make sure that SkiaSharp is properly supporting native library trimming/exclusion.