[camera_platform_interface] Stable null safety release. (flutter#3610)

* Stable null safety release camera_platform_interface

* Update minimum plugin_platform_interface version

* Update version of cross_file to 0.3.1

packages/camera/camera_platform_interface/CHANGELOG.md

@@ -1,6 +1,6 @@
-## 2.0.0-nullsafety
+## 2.0.0
 
-- Migrate to null safety.
+- Stable null safety release.
 
 ## 1.6.0
 

packages/camera/camera_platform_interface/pubspec.yaml

@@ -3,22 +3,22 @@ description: A common platform interface for the camera plugin.
 homepage: https://github.com/flutter/plugins/tree/master/packages/camera/camera_platform_interface
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 2.0.0-nullsafety
+version: 2.0.0
 
 dependencies:
   flutter:
     sdk: flutter
-  meta: ^1.3.0-nullsafety.6
-  plugin_platform_interface: ^1.1.0-nullsafety.2
-  cross_file: ^0.3.0-nullsafety
-  stream_transform: ^2.0.0-nullsafety.0
+  meta: ^1.3.0
+  plugin_platform_interface: ">=1.0.0 <3.0.0"
+  cross_file: ^0.3.1
+  stream_transform: ^2.0.0
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  async: ^2.5.0-nullsafety.3
-  pedantic: ^1.10.0-nullsafety.3
+  async: ^2.5.0
+  pedantic: ^1.10.0
 
 environment:
-  sdk: '>=2.12.0-0 <3.0.0'
+  sdk: '>=2.12.0-259.9.beta <3.0.0'
   flutter: ">=1.22.0"