[web] dispatch corresponding keyup events in text editing integrations (#136874)

https://github.com/flutter/engine/pull/46829 changed event handling
sequence on web so that KeyboardBinding/RawKeyboard handles the text
event first before it reaches IME. That means when dispatching
synthetised events to IME every keydown event must have a corresponding
keyup, otherwise consistency assertions in `KeyboardBindings` are
triggered.

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[test-exempt].
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dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration.dart

@@ -80,12 +80,17 @@ void main() {
     expect(textFormFieldsFinder, findsOneWidget);
     await tester.tap(find.byKey(const Key('input2')));
 
-    // // Press Tab. This should trigger `onFieldSubmitted` of TextField.
+    // Press Tab. This should trigger `onFieldSubmitted` of TextField.
     final InputElement input = findElements('input')[0] as InputElement;
     dispatchKeyboardEvent(input, 'keydown', <String, dynamic>{
       'keyCode': 13, // Enter.
       'cancelable': true,
     });
+    // Release Tab.
+    dispatchKeyboardEvent(input, 'keyup', <String, dynamic>{
+      'keyCode': 13, // Enter.
+      'cancelable': true,
+    });
 
     await tester.pumpAndSettle();
 
@@ -118,6 +123,14 @@ void main() {
       'cancelable': true,
       'composed': true,
     });
+    // Release tab.
+    dispatchKeyboardEvent(input, 'keyup', <String, dynamic>{
+      'key': 'Tab',
+      'code': 'Tab',
+      'bubbles': true,
+      'cancelable': true,
+      'composed': true,
+    });
 
     await tester.pumpAndSettle();
 
@@ -165,6 +178,14 @@ void main() {
       'cancelable': true,
       'composed': true,
     });
+    // Release Tab.
+    dispatchKeyboardEvent(input, 'keyup', <String, dynamic>{
+      'key': 'Tab',
+      'code': 'Tab',
+      'bubbles': true,
+      'cancelable': true,
+      'composed': true,
+    });
 
     await tester.pumpAndSettle();