e9965b2d07
Eliminates some cases where `FlutterViewController` was relying on `FlutterEngine` internals: * `[FlutterEngine shell]` * `[FlutterEngine platformView]` * `[FlutterEngine iosPlatformView]` Instead, `FlutterEngine` now exposes: * `installFirstFrameCallback:` * `enableSemantics:withFlags:` * `notifyViewCreated` * `notifyViewDestroyed` * `waitForFirstFrameSync:callback:` Also fixes a couple cases where we were relying on transitive header includes: * `FlutterAppController` relied on `FlutterViewController_Internal.h` for `sendDeepLinkToFramework:completionHandler:` This is a refactoring followup to https://github.com/flutter/engine/pull/57099 that introduces no semantic changes. [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style