transparent safearea not work may be flutter official did fix

transparent SafeareaView not work may be flutter official did fix

[the merged code](https://github.com/flutter/engine/pull/16208/commits/7b6d794f0870a84e0dfbb6fef8d17390cb03110e)

the [origin issues](https://github.com/flutter/flutter/issues/46060)

BoostFlutterActivity.java
```
private void configureWindowForTransparency() {
BoostFlutterActivity.BackgroundMode backgroundMode = this.getBackgroundMode();
if (backgroundMode == BoostFlutterActivity.BackgroundMode.transparent) {
this.getWindow().setBackgroundDrawable(new ColorDrawable(0));
this.getWindow().setFlags(512, 512);
}
}
```

### my example code, whick BoostFlutterActivity.BackgroundMode.opaque is ok
my commit is [here](https://github.com/krmao/template/commit/17786cb2220a73ba5d39fbd934d03d1ceb6718e1#diff-5100788880182e2c732f9baec7da19b353e7eab621daff49dfa5937a81782e79)

```
% flutter doctor -v
[✓] Flutter (Channel unknown, 1.22.4, on Mac OS X 10.15.7 19H2 darwin-x64, locale zh-Hans-CN)
• Flutter version 1.22.4 at /Users/krmao/fvm/versions/1.22.4
• Framework revision 1aafb3a8b9 (8 weeks ago), 2020-11-13 09:59:28 -0800
• Engine revision 2c956a31c0
• Dart version 2.10.4

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.0)
• Android SDK at /Users/krmao/sdks/android/sdk
• Platform android-30, build-tools 30.0.0
• ANDROID_HOME = /Users/krmao/sdks/android/sdk
• Java binary at: /Applications/Android Studio 4.1.1.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.2)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 12.2, Build version 12B45b
• CocoaPods version 1.10.0

[!] Android Studio (version 4.1)
• Android Studio at /Applications/Android Studio 4.1.1.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-b3-6915495)

[✓] Android Studio (version 3.6)
• Android Studio at /Applications/Android Studio 3.6.3.app/Contents
• Flutter plugin version 49.0.1
• Dart plugin version 192.8052
• Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)

[✓] IntelliJ IDEA Ultimate Edition (version 2019.3.3)
• IntelliJ at /Applications/IntelliJ IDEA.app
• Flutter plugin version 45.1.2
• Dart plugin version 193.6494.35

[!] VS Code (version 1.52.1)
• VS Code at /Applications/Visual Studio Code.app/Contents
✗ Flutter extension not installed; install from
https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[✓] Connected device (1 available)
• CLT AL01 (mobile) • AKC7N19118000852 • android-arm64 • Android 10 (API 29)

! Doctor found issues in 2 categories.
```

```
flutter_boost:
git:
url: 'https://github.com/alibaba/flutter_boost.git'
ref: 'v1.22.4-hotfixes'
```