Add Points collection observability support for Polygon and Polyline

[SKProCH]

What does the pull request do?

Add Points binding observability support for Polygon and Polyline

What is the current behavior?

When ObservableCollection was bound to Points property, updating collection does not updates the geometry. See #3623

What is the updated/expected behavior with this PR?

When ObservableCollection was bound to Points property, updating collection updates the geometry (and control actially re-rendered with a new geometry)

Checklist

• Added unit tests (if possible)? (not possible)
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

None

Fixed issues

Fixes #3623

[maxkatz6]

Can you add a simple unit test for this scenario?
It should be enough to check if shape.IsMeasureValid property returns false value.

[SKProCH]

@maxkatz6 done

[maxkatz6]

@SKProCH ok... I have checked a little, and noticed that change notification should have already been working with this code:
https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Base/Media/PolylineGeometry.cs#L100-L107

But as you can see, it only supported IAvaloniaList. So, this PR should instead fix PolylineGeometry/PolygonGeometry not respecting INotifyCollectionChanged.

[SKProCH]

The problem with this geometry is under the hood implementation. We create a new Points collection inside geometry ctor:

Avalonia/src/Avalonia.Base/Media/PolylineGeometry.cs

Lines 46 to 48 in 4c949ee

	public PolylineGeometry(IEnumerable<Point> points, bool isFilled)
	{
	_points = new Points(points);

Points its just a sealed inheritor of AvaloniaList:

Avalonia/src/Avalonia.Base/Points.cs

Lines 6 to 16 in 4c949ee

	public sealed class Points : AvaloniaList<Point>
	{
	public Points()
	{
	}
	public Points(IEnumerable<Point> points) : base(points)
	{
	}

But as we can see inside AvaloniaList's ctor, it copying collection content from the collection parameter:

Avalonia/src/Avalonia.Base/Collections/AvaloniaList.cs

Lines 76 to 79 in 4c949ee

	public AvaloniaList(IEnumerable<T> items)
	{
	_inner = new List<T>(items);
	}

So, at the moment where we create an Points collection inside of Geometry ctor we just copying the elements of the original collection, and we don't have reference to original collection and the changes doesn't propagated to the Points.

It's actually has the same effect if we just call .ToList() to original collection.

So, currently there is no actual benefits of changing OnPointsChanged implementation as you suggest.

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0046333-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[maxkatz6]

Try to replace

return new PolylineGeometry(Points, true);

with

return new PolylineGeometry
{
    Points = Points,
    IsFilled = true
}

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0046389-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0046393-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[SKProCH]

Actually some of tests failing, i'll fix that a little later

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0046408-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0046473-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0046475-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]