[featurePR]使FlutterBoost支持沉浸式状态栏各页面设置状态共享，保持和dart层一致的功能

**Old logic：**
1、flutterA进入flutterB的activity，B销毁了A的platformPlugin
2、从B返回A，这个时候A页面检测到platformPlugin为空，重新创建platformPlugin【状态栏主题为初态，丢失之前的设置】；
3、A页面在onResume调用this.platformPlugin.updateSystemUiOverlays()，导致状态栏颜色重置

**New logic：**
1、定制FlutterBoostPlatformPlugin，destroy的时候保存状态栏状态【currentTheme和enabledOverlays】
2、创建FlutterBoostPlatformPlugin的时候进行currentTheme和enabledOverlays的恢复，保证状态栏沉浸式状态始终与dart保持同步

Start with the FlutterBoostPlatformPlugin lifecycle, especially destroy, creation, onResume, and updateSystemUiOverlays(). Trace how currentTheme and enabledOverlays are handled across plugin recreation. Done means the saved status-bar state is restored on creation and remains synchronized with the Dart layer when returning between pages.

Written by the indexing model from the issue text.