[various] Prepare plugin repo for binding API improvements

Since plugins also have to work with the stable branch, we can't actually take advantage of the changes right away, so we muddle the issue in the meantime.

Prep for flutter/flutter#83843

See also flutter#4136, flutter#4137

Author: Hixie

packages/camera/camera/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.8.2
+
+* Silenced warnings that may occur during build when using a very
+  recent version of Flutter relating to null safety.
+
 ## 0.8.1+3
 
 * Do not change camera orientation when iOS device is flat.

packages/camera/camera/example/lib/main.dart

@@ -98,7 +98,7 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
 
   @override
   void dispose() {
-    WidgetsBinding.instance?.removeObserver(this);
+    _ambiguate(WidgetsBinding.instance)?.removeObserver(this);
     _flashModeControlRowAnimationController.dispose();
     _exposureModeControlRowAnimationController.dispose();
     super.dispose();

packages/camera/camera/pubspec.yaml

@@ -4,7 +4,7 @@ description: A Flutter plugin for getting information about and controlling the
   and streaming image buffers to dart.
 repository: https://github.com/flutter/plugins/tree/master/packages/camera/camera
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.8.1+3
+version: 0.8.2
 
 environment:
   sdk: ">=2.12.0 <3.0.0"

packages/video_player/video_player/test/video_player_test.dart

@@ -856,7 +856,16 @@ class FakeEventsChannel {
   }
 
   void _sendMessage(ByteData data) {
-    ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage(
-        eventsMethodChannel.name, data, (ByteData? data) {});
+    _ambiguate(ServicesBinding.instance)!
+        .defaultBinaryMessenger
+        .handlePlatformMessage(
+            eventsMethodChannel.name, data, (ByteData? data) {});
   }
 }
+
+/// This allows a value of type T or T? to be treated as a value of type T?.
+///
+/// We use this so that APIs that have become non-nullable can still be used
+/// with `!` and `?` on the stable branch.
+// TODO(ianh): Remove this once we roll stable in late 2021.
+T? _ambiguate<T>(T? value) => value;