What would you like to be added:

Support for LinearGradientBrush for borders, including RenderTransform support

Primary need is currently iOS, macOS and WASM

Why is this needed:

Many WinUI 2.6 styles use LinearGradientBrush to simulate "elevation".

For which Platform:

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