Repository: flutter
Issue: CupertinoTextSelectionToolbar doesn't vertically centre align text in Chinese language
Labels: a: text input,framework,a: internationalization,f: cupertino,has reproducible steps,P2,found in release: 3.3,found in release: 3.7,team-design,triaged-design

1. Setup localizations settings
pubspec.yaml
```
  flutter_localizations:
    sdk: flutter
```
MyApp
```
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      localizationsDelegates: [
        GlobalCupertinoLocalizations.delegate,
        DefaultCupertinoLocalizations.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],
      supportedLocales: [
        const Locale('zh', 'CH'),
        const Locale('en', 'US'),
      ],
      locale: Locale('zh', 'CH'),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}
```
2. Put a TextField to page.
```
Padding(
              padding: EdgeInsets.fromLTRB(20, 0, 20, 0),
              child: TextField(),
            ),
```
3. Double tap TextField will show CupertinoTextSelectionToolbar in Chinese, it will not display center.
<img width="406" alt="WX20200715-172840@2x" src="https://user-images.githubusercontent.com/11239033/87528825-a7d50f00-c6c0-11ea-8de4-12fbf416ef22.png">

when I change the language to en, it will display correct.
```
      locale: Locale('en', 'US'),
      // locale: Locale('zh', 'CH'),
```
<img width="442" alt="WX20200715-173057@2x" src="https://user-images.githubusercontent.com/11239033/87529029-f682a900-c6c0-11ea-995a-1f736a1ee052.png">

flutter doctor -v
```
[✓] Flutter (Channel stable, v1.17.5, on Mac OS X 10.15.5 19F101, locale en)
    • Flutter version 1.17.5 at /Users/wangyu/Yu/flutter
    • Framework revision 8af6b2f038 (2 weeks ago), 2020-06-30 12:53:55 -0700
    • Engine revision ee76268252
    • Dart version 2.8.4

[!] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    • Android SDK at /Users/wangyu/Library/Android/sdk
    • Platform android-29, build-tools 29.0.3
    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)
    ✗ Android license status unknown.
      Try re-installing or updating your Android SDK Manager.
      See https://developer.android.com/studio/#downloads or visit visit
      https://flutter.dev/docs/get-started/install/macos#android-setup for
      detailed instructions.

 
[✓] Xcode - develop for iOS and macOS (Xcode 11.5)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 11.5, Build version 11E608c
    • CocoaPods version 1.9.1

[!] Android Studio (version 4.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)

[✓] IntelliJ IDEA Ultimate Edition (version 2019.2.2)
    • IntelliJ at /Applications/IntelliJ IDEA.app
    • Flutter plugin version 31.3.3
    • Dart plugin version 182.5124

[✓] VS Code (version 1.47.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.12.2

[✓] Connected device (1 available)
    • iPhone 11 Pro Max • B3A87334-6C79-4ADD-A38E-BF76EC71D171 • ios •
      com.apple.CoreSimulator.SimRuntime.iOS-13-5 (simulator)

! Doctor found issues in 2 categories.
```