Fix SelectableTextBlock selection

src/Avalonia.Controls/SelectableTextBlock.cs

@@ -18,10 +18,10 @@ namespace Avalonia.Controls
     public class SelectableTextBlock : TextBlock, IInlineHost
     {
         public static readonly StyledProperty<int> SelectionStartProperty =
-            TextBox.SelectionStartProperty.AddOwner<SelectableTextBlock>(new(coerce: TextBox.CoerceCaretIndex));
+            TextBox.SelectionStartProperty.AddOwner<SelectableTextBlock>();
 
         public static readonly StyledProperty<int> SelectionEndProperty =
-            TextBox.SelectionEndProperty.AddOwner<SelectableTextBlock>(new(coerce: TextBox.CoerceCaretIndex));
+            TextBox.SelectionEndProperty.AddOwner<SelectableTextBlock>();
 
         public static readonly DirectProperty<SelectableTextBlock, string> SelectedTextProperty =
             AvaloniaProperty.RegisterDirect<SelectableTextBlock, string>(
@@ -228,7 +228,7 @@ namespace Avalonia.Controls
         {
             base.OnPointerPressed(e);
 
-            var text = Text;
+            var text = HasComplexContent ? Inlines.Text : Text;
             var clickInfo = e.GetCurrentPoint(this);
 
             if (text != null && clickInfo.Properties.IsLeftButtonPressed)
@@ -314,7 +314,7 @@ namespace Avalonia.Controls
             // selection should not change during pointer move if the user right clicks
             if (e.Pointer.Captured == this && e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
             {
-                var text = Text;
+                var text = HasComplexContent ? Inlines.Text : Text;
                 var padding = Padding;
 
                 var point = e.GetPosition(this) - new Point(padding.Left, padding.Top);
@@ -397,7 +397,10 @@ namespace Avalonia.Controls
 
         private string GetSelection()
         {
-            var textLength = Text?.Length ?? 0;
+            var text = HasComplexContent ? Inlines.Text : Text;
+
+            var textLength = text?.Length ?? 0;
+
             if (textLength == 0)
             {
                 return "";
@@ -415,7 +418,7 @@ namespace Avalonia.Controls
 
             var length = Math.Max(0, end - start);
 
-            var selectedText = Text!.Substring(start, length);
+            var selectedText = text!.Substring(start, length);
 
             return selectedText;
         }