feat!: add aria-hidden="true" to hr component by default (#22571)

* feat!: add aria-hidden="true" to hr component by default

The <hr> element is announced as "Horizontal Splitter" by screen readers
(e.g., VoiceOver on macOS), but in most cases it's used for visual
purposes only. Adding aria-hidden="true" by default improves
accessibility by preventing screen readers from announcing it.

Users can still override this if needed by removing the attribute.

Fixes #14881

Author: Artur-

flow-html-components/src/main/java/com/vaadin/flow/component/html/Hr.java

@@ -32,5 +32,6 @@ public class Hr extends HtmlComponent {
      */
     public Hr() {
         super();
+        getElement().setAttribute("aria-hidden", "true");
     }
 }

flow-html-components/src/test/java/com/vaadin/flow/component/html/HrTest.java

@@ -15,6 +15,9 @@
  */
 package com.vaadin.flow.component.html;
 
+import org.junit.Assert;
+import org.junit.Test;
+
 public class HrTest extends ComponentTest {
 
     // Actual test methods in super class
@@ -23,4 +26,11 @@ public class HrTest extends ComponentTest {
     protected void addProperties() {
         // Component defines no new properties
     }
+
+    @Test
+    public void ariaHiddenSetByDefault() {
+        Hr hr = new Hr();
+        Assert.assertEquals("true",
+                hr.getElement().getAttribute("aria-hidden"));
+    }
 }