Feat/19059 add automation for validation error (#19161)

* try to add Automation/Peers/DataValidationErrorsAutomationPeer.cs

* add missing file

* change to use .ToString() instead of fileter only string type

* 19059 resolve maxkatz6's comment

* 19059 resolve comment

* 19059 check if GetTip return null or whitespace

* 19059 take the error higher piority than the tooltip

---------

Co-authored-by: Long Bui <long.bui@taitcommunications.com>
Co-authored-by: Max Katz <maxkatz6@outlook.com>

src/Avalonia.Controls/Automation/Peers/ControlAutomationPeer.cs

@@ -117,15 +117,22 @@ namespace Avalonia.Automation.Peers
             return result;
         }
         protected override string? GetHelpTextCore()
-        {          
+        {
             var result = AutomationProperties.GetHelpText(Owner);
 
+            if (string.IsNullOrWhiteSpace(result))
+            {
+                var errors = DataValidationErrors.GetErrors(Owner);
+                var errorsStringList = errors?.Select(x => x.ToString());
+                result = errorsStringList != null ? string.Join(Environment.NewLine, errorsStringList.ToArray()) : null;
+            }
+
             if (string.IsNullOrWhiteSpace(result))
             {
                 result = ToolTip.GetTip(Owner) as string;
             }
 
-            return result;          
+            return result;
         }
         protected override AutomationPeer? GetParentCore()
         {

src/Avalonia.Controls/DataValidationErrors.cs

@@ -5,7 +5,6 @@ using Avalonia.Reactive;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
-
 namespace Avalonia.Controls
 {
     /// <summary>