Add Transform and RelativeTransform properties for Brush'es

[wieslawsoltes]

Is your feature request related to a problem? Please describe.

Add support for Transform and RelativeTransform (not sure if this one is needed) property for Brush'es (LinearGradientBrush, RadialGradientBrush and VisualBrush).

• Brush.Transform Property
• Brush Transformation Overview

Describe the solution you'd like

Add to Brush two transformation properties: Transform and RelativeTransform. The properties enable rotate, scale, skew, and translate a brush's contents.

Describe alternatives you've considered

Did try manually transform brush properties, but that doesn't really work.

Additional context

It is very useful for example when converting Svg paint servers to Avalonia brushes. As paint server can use user space coordinates and bounding box coordinates and can have transform property set for brush transformations. Right now I am using LinearGradientBrush, RadialGradientBrush and VisualBrush and all of them require transform.

SkiaSharp support local matrix parameter when creating shaders for brushes:

• CreateLinearGradient

• CreateRadialGradient

• CreateTwoPointConicalGradient

• CreatePicture

That is what I use for Svg rendering.

I am converting the svg brushes to WPF xaml here https://github.com/wieslawsoltes/SvgGradientsDemo for reference.

[maxkatz6]

Same issue #5768

[wieslawsoltes]

Same issue #5768

I should have searched issue before posting this.