Fix ios voiceover (for safari >13.4)

lib/web_ui/lib/src/engine/semantics/semantics_helper.dart

@@ -256,8 +256,11 @@ class MobileSemanticsEnabler extends SemanticsEnabler {
   @override
   bool tryEnableSemantics(html.Event event) {
     if (_schedulePlaceholderRemoval) {
-      final bool removeNow =
-          (browserEngine != BrowserEngine.webkit || event.type == 'touchend');
+      // The event type can also be click for VoiceOver.
+      final bool removeNow = (browserEngine != BrowserEngine.webkit ||
+          event.type == 'touchend' ||
+          event.type == 'pointerup' ||
+          event.type == 'click');
       if (removeNow) {
         _semanticsPlaceholder!.remove();
         _semanticsPlaceholder = null;
@@ -280,10 +283,16 @@ class MobileSemanticsEnabler extends SemanticsEnabler {
       return true;
     }
 
+    // ios-safari browsers which starts sending `pointer` events instead of
+    // `touch` events. (Tested with 12.1 which uses touch events vs 13.5
+    // which uses pointer events.)
     const Set<String> kInterestingEventTypes = <String>{
       'click',
       'touchstart',
       'touchend',
+      'pointerdown',
+      'pointermove',
+      'pointerup',
     };
 
     if (!kInterestingEventTypes.contains(event.type)) {
@@ -333,6 +342,11 @@ class MobileSemanticsEnabler extends SemanticsEnabler {
           final html.TouchEvent touch = event as html.TouchEvent;
           activationPoint = touch.changedTouches!.first.client;
           break;
+        case 'pointerdown':
+        case 'pointerup':
+          final html.PointerEvent touch = event as html.PointerEvent;
+          activationPoint = new html.Point(touch.client.x, touch.client.y);
+          break;
         default:
           // The event is not relevant, forward to framework as normal.
           return true;
@@ -341,9 +355,11 @@ class MobileSemanticsEnabler extends SemanticsEnabler {
       final html.Rectangle<num> activatingElementRect =
           domRenderer.glassPaneElement!.getBoundingClientRect();
       final double midX = (activatingElementRect.left +
-          (activatingElementRect.right - activatingElementRect.left) / 2).toDouble();
+              (activatingElementRect.right - activatingElementRect.left) / 2)
+          .toDouble();
       final double midY = (activatingElementRect.top +
-          (activatingElementRect.bottom - activatingElementRect.top) / 2).toDouble();
+              (activatingElementRect.bottom - activatingElementRect.top) / 2)
+          .toDouble();
       final double deltaX = activationPoint.x.toDouble() - midX;
       final double deltaY = activationPoint.y.toDouble() - midY;
       final double deltaSquared = deltaX * deltaX + deltaY * deltaY;

lib/web_ui/test/engine/semantics/semantics_helper_test.dart

@@ -9,6 +9,8 @@ import 'package:test/bootstrap/browser.dart';
 import 'package:test/test.dart';
 import 'package:ui/src/engine.dart';
 
+const PointerSupportDetector _defaultSupportDetector = PointerSupportDetector();
+
 void main() {
   internalBootstrapBrowserTest(() => testMain);
 }
@@ -151,15 +153,22 @@ void testMain() {
         skip: browserEngine == BrowserEngine.webkit);
 
     test('Not relevant events should be forwarded to the framework', () async {
-      final html.Event event = html.TouchEvent('touchcancel');
+      html.Event event;
+      if (_defaultSupportDetector.hasPointerEvents) {
+        event = html.PointerEvent('pointermove');
+      } else if (_defaultSupportDetector.hasTouchEvents) {
+        event = html.TouchEvent('touchcancel');
+      } else {
+        event = html.MouseEvent('mousemove');
+      }
+
       bool shouldForwardToFramework =
           mobileSemanticsEnabler.tryEnableSemantics(event);
 
       expect(shouldForwardToFramework, true);
-    },
-        // TODO(nurhan): https://github.com/flutter/flutter/issues/50590
-        // TODO(nurhan): https://github.com/flutter/flutter/issues/46638
-        // TODO(nurhan): https://github.com/flutter/flutter/issues/50754
-        skip: browserEngine != BrowserEngine.blink);
-  });
+    });
+  },  // Run the `MobileSemanticsEnabler` only on mobile browsers.
+      skip: operatingSystem == OperatingSystem.linux ||
+          operatingSystem == OperatingSystem.macOs ||
+          operatingSystem == OperatingSystem.windows);
 }