Fixes relative brush mapping mode (#14598)

* Fixed relative mapping mode for brushes (skia only, pending radial)

* Implemented separate RadiusX/RadiusY with proper mapping modes for RadialGradientBrush

* tests for conic brush

* Added tests for geometry drawing

* Updated DrawingBrush test image since it now matches WPF

* Update obsolete property usage

* Fixed D2D, updated radial test with D2D results that actually match WPF ones

* Fixed RadiusX/Y for radial gradients with non-centered origin

* Updated obsolete property usage

* Code cleanup

* Typo

* ApiDiff suppression

* Removed files for skipped test

* More info in obsoletion warning

* clarify

---------

Co-authored-by: Jumar Macato <16554748+jmacato@users.noreply.github.com>

Avalonia.Desktop.slnf

@@ -11,6 +11,7 @@
       "samples\\IntegrationTestApp\\IntegrationTestApp.csproj",
       "samples\\MiniMvvm\\MiniMvvm.csproj",
       "samples\\ReactiveUIDemo\\ReactiveUIDemo.csproj",
+      "samples\\RenderDemo\\RenderDemo.csproj",
       "samples\\SampleControls\\ControlSamples.csproj",
       "samples\\Sandbox\\Sandbox.csproj",
       "src\\Avalonia.Base\\Avalonia.Base.csproj",