Fix a few prefer_const_declarations and avoid_redundant_argument_values. (flutter#92929)

Author: scheglov

packages/flutter/test/cupertino/text_field_test.dart

@@ -27,7 +27,7 @@ import '../widgets/editable_text_utils.dart' show OverflowWidgetTextEditingContr
 import '../widgets/semantics_tester.dart';
 
 // On web, the context menu (aka toolbar) is provided by the browser.
-final bool isContextMenuProvidedByPlatform = isBrowser;
+const bool isContextMenuProvidedByPlatform = isBrowser;
 
 class MockTextSelectionControls extends TextSelectionControls {
   @override

packages/flutter/test/material/text_field_test.dart

@@ -31,10 +31,10 @@ import 'feedback_tester.dart';
 typedef FormatEditUpdateCallback = void Function(TextEditingValue, TextEditingValue);
 
 // On web, the context menu (aka toolbar) is provided by the browser.
-final bool isContextMenuProvidedByPlatform = isBrowser;
+const bool isContextMenuProvidedByPlatform = isBrowser;
 
 // On web, key events in text fields are handled by the browser.
-final bool areKeyEventsHandledByPlatform = isBrowser;
+const bool areKeyEventsHandledByPlatform = isBrowser;
 
 class MaterialLocalizationsDelegate extends LocalizationsDelegate<MaterialLocalizations> {
   @override

packages/flutter/test/painting/image_provider_network_image_test.dart

@@ -36,7 +36,7 @@ void main() {
   });
 
   test('Expect thrown exception with statusCode - evicts from cache and drains', () async {
-    final int errorStatusCode = HttpStatus.notFound;
+    const int errorStatusCode = HttpStatus.notFound;
     const String requestUrl = 'foo-url';
 
     httpClient.request.response.statusCode = errorStatusCode;

packages/flutter_localizations/test/material/date_picker_test.dart

@@ -13,7 +13,7 @@ void main() {
   late DateTime initialDate;
 
   setUp(() {
-    firstDate = DateTime(2001, DateTime.january);
+    firstDate = DateTime(2001);
     lastDate = DateTime(2031, DateTime.december, 31);
     initialDate = DateTime(2016, DateTime.january, 15);
   });