[material_ui] Remove widgets import in data_table_test.dart, switch_test.dart and tooltip_theme_test.dart (#12031)

Part of flutter/flutter#182636 and flutter/flutter#188395

This PR:
* Removed the cross-import of `widgets/semantics_tester.dart`.
* Removed @Skip tag, all tests in this file has passed. `semantics_tester.dart` has existed in material_ui, so we can directly import `semantics_tester.dart`;
* Moved the file to `test/` folder.

## Pre-Review Checklist

Author: QuncCccccc

…rily_disabled_tests/data_table_test.dart …es/material_ui/test/data_table_test.dartpackages/material_ui/temporarily_disabled_tests/data_table_test.dart renamed to packages/material_ui/test/data_table_test.dart packages/material_ui/temporarily_disabled_tests/data_table_test.dart renamed to packages/material_ui/test/data_table_test.dart

@@ -2,23 +2,20 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-@Skip(
-  'This file is skipped due to a cross-import that needs to be fixed. Tracked in https://github.com/flutter/flutter/issues/177028.',
-)
 @TestOn('!chrome')
 library;
 
 import 'dart:math' as math;
 
 import 'package:flutter/foundation.dart' show kIsWeb;
 import 'package:flutter/gestures.dart';
-import 'package:material_ui/material_ui.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:material_ui/material_ui.dart';
 import 'package:vector_math/vector_math_64.dart' show Matrix3;
 
-import '../widgets/semantics_tester.dart';
 import 'data_table_test_utils.dart';
+import 'semantics_tester.dart';
 
 void main() {
   testWidgets('DataTable control test', (WidgetTester tester) async {

…porarily_disabled_tests/switch_test.dart …ckages/material_ui/test/switch_test.dartpackages/material_ui/temporarily_disabled_tests/switch_test.dart renamed to packages/material_ui/test/switch_test.dart packages/material_ui/temporarily_disabled_tests/switch_test.dart renamed to packages/material_ui/test/switch_test.dart

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-@Skip(
-  'This file is skipped due to a cross-import that needs to be fixed. Tracked in https://github.com/flutter/flutter/issues/177028.',
-)
 // This file is run as part of a reduced test set in CI on Mac and Windows
 // machines.
 @Tags(<String>['reduced-test-set'])
@@ -16,12 +13,12 @@ import 'dart:ui' as ui;
 import 'package:cupertino_ui/cupertino_ui.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
-import 'package:material_ui/material_ui.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:material_ui/material_ui.dart';
 
-import '../widgets/semantics_tester.dart';
+import 'semantics_tester.dart';
 
 void main() {
   final theme = ThemeData();

…y_disabled_tests/tooltip_theme_test.dart …material_ui/test/tooltip_theme_test.dartpackages/material_ui/temporarily_disabled_tests/tooltip_theme_test.dart renamed to packages/material_ui/test/tooltip_theme_test.dart packages/material_ui/temporarily_disabled_tests/tooltip_theme_test.dart renamed to packages/material_ui/test/tooltip_theme_test.dart

@@ -2,15 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-@Skip(
-  'This file is skipped due to a cross-import that needs to be fixed. Tracked in https://github.com/flutter/flutter/issues/177028.',
-)
 import 'package:flutter/gestures.dart';
-import 'package:material_ui/material_ui.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
-import '../widgets/semantics_tester.dart';
+import 'package:material_ui/material_ui.dart';
+
+import 'semantics_tester.dart';
 
 const String tooltipText = 'TIP';
 const double _customPaddingValue = 10.0;