AvaloniaList compile time parsing

[maxkatz6]

What does the pull request do?

Instead of relying on runtime parsing which would bring unsafe AvaloniaListConverter (because of TypeConverters with reflection), attempt to do it compile time for prepared types.

Initially I added this attribute for Classes property, which doesn't use ',' as a separator and ' ' is instead, but @grokys already has redone how Classes are parsed in compile time and it has a way more specific logic now.
This attribute can be removed now, if we define "," as a separator for all AvaloniaLists and not just default.

Fixed issues

Fixes #10109

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0033524-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[kekekeks]

I wonder if it makes sense to parse into T[] instead of AvaloniaList<T> when property is IList<T>-typed

[maxkatz6]

@kekekeks done, also kekekeks/XamlX#86

[maxkatz6]

Not related to this PR, but changes nullability of points property to be consistent with PolyLineSegment/Geometry.

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0033565-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[robloo]

Not a huge fan of going from a clear Points collection to IList<Point>. Seems like a step backwards from an API standpoint. We really shouldn't be passing around IList following other XAML framework conventions.

WPF:
https://learn.microsoft.com/en-us/dotnet/api/system.windows.shapes.polygon.points?view=netframework-4.8