Fix DefinitionList parsing

src/Avalonia.Controls/DefinitionList.cs

@@ -1,9 +1,11 @@
 using System.Collections;
 using System.Collections.Specialized;
 using Avalonia.Collections;
+using Avalonia.Metadata;
 
 namespace Avalonia.Controls
 {
+    [AvaloniaList(Separators = new [] { ",", " " })]
     public abstract class DefinitionList<T> : AvaloniaList<T> where T : DefinitionBase
     {
         public DefinitionList()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BasicTests.cs

@@ -261,6 +261,37 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             var grid = AvaloniaRuntimeXamlLoader.Parse<Grid>(xaml);
 
 
+            Assert.Equal(4, grid.ColumnDefinitions.Count);
+            Assert.Equal(4, grid.RowDefinitions.Count);
+
+            var expected1 = new GridLength(100);
+            var expected2 = GridLength.Auto;
+            var expected3 = new GridLength(1, GridUnitType.Star);
+            var expected4 = new GridLength(100, GridUnitType.Star);
+
+            Assert.Equal(expected1, grid.ColumnDefinitions[0].Width);
+            Assert.Equal(expected2, grid.ColumnDefinitions[1].Width);
+            Assert.Equal(expected3, grid.ColumnDefinitions[2].Width);
+            Assert.Equal(expected4, grid.ColumnDefinitions[3].Width);
+
+            Assert.Equal(expected1, grid.RowDefinitions[0].Height);
+            Assert.Equal(expected2, grid.RowDefinitions[1].Height);
+            Assert.Equal(expected3, grid.RowDefinitions[2].Height);
+            Assert.Equal(expected4, grid.RowDefinitions[3].Height);
+        }
+        
+        [Fact]
+        public void Grid_Row_Col_Definitions_Are_Parsed_Space_Delimiter()
+        {
+            var xaml = @"
+<Grid xmlns='https://github.com/avaloniaui'
+        ColumnDefinitions='100 Auto * 100*'
+        RowDefinitions='100 Auto * 100*'>
+</Grid>";
+
+            var grid = AvaloniaRuntimeXamlLoader.Parse<Grid>(xaml);
+
+
             Assert.Equal(4, grid.ColumnDefinitions.Count);
             Assert.Equal(4, grid.RowDefinitions.Count);