Leave the windowing bridge out of the 0.2.7 package

It imports Flutter's internal windowing libraries as they are on the main
channel; on stable they differ, the library does not analyze, and pub refuses
the package. A .pubignore does not help, the validator analyzes all of lib/ on
disk. main keeps the library.

Author: lijy91

README-ZH.md

@@ -48,6 +48,9 @@ DragToResizeArea(
 
 ### 用 Flutter 渲染的第二个窗口
 
+> **暂未包含在 pub.dev 的包里。** `package:nativeapi/windowing.dart` 跟随 Flutter main 通道，在 stable 上无法通过分析，
+> 所以 0.2.7 发布时没有带上它。要使用它，请改为依赖 [git 仓库](https://github.com/libnativeapi/nativeapi-flutter)。
+
 `Window.create()` 打开的是一个不含 Flutter 视图的原生空窗口。要在第二个窗口里渲染 widget，请用 Flutter 的多窗口 API 创建窗口，再把 controller 交给 nativeapi：
 
 ```dart

README.md

@@ -48,6 +48,10 @@ Both widgets use `WindowManager.instance.getCurrent()` unless a `window` is pass
 
 ### Flutter-rendered secondary windows
 
+> **Not in the pub.dev package yet.** `package:nativeapi/windowing.dart` follows Flutter's
+> main channel and does not analyze on stable, so 0.2.7 ships without it. To use it, depend
+> on the [git repository](https://github.com/libnativeapi/nativeapi-flutter) instead.
+
 `Window.create()` opens a bare native window with no Flutter view in it. To render widgets in a second window, create it with Flutter's multi-window API and hand the controller to nativeapi:
 
 ```dart

packages/nativeapi/CHANGELOG.md

@@ -1,13 +1,3 @@
-## Unreleased
-
-* Add `package:nativeapi/windowing.dart`: `controller.nativeWindow` / `nativeWindowOf()`
-  turn a window created with Flutter's experimental multi-window API into a nativeapi
-  `Window`, so Flutter-rendered secondary windows can be styled, positioned and observed
-  from Dart alone. Kept out of the main library because it needs the Flutter main channel
-  with `--enable-windowing`.
-  Not part of the pub.dev package yet: it does not analyze on stable Flutter, so use a git
-  dependency for it.
-
 ## 0.2.7
 
 * Add `WindowCreatedEvent` and `WindowClosedEvent`. `WindowManager.addListener` now reports