[battery] Bump version for NNBD stable (flutter#3594)

Also replaces Mockito with test/Fake since the usage is a simple fake.

Author: stuartmorgan-g

packages/battery/battery/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 2.0.0-nullsafety
+## 2.0.0
 
 * Migrate to null safety.
 

packages/battery/battery/example/pubspec.yaml

@@ -17,11 +17,11 @@ dev_dependencies:
     sdk: flutter
   integration_test:
     path: ../../../integration_test
-  pedantic: ^1.10.0-nullsafety
+  pedantic: ^1.10.0
 
 flutter:
   uses-material-design: true
 
 environment:
-  sdk: ">=2.12.0-0 <3.0.0"
+  sdk: ">=2.12.0-259.9.beta <3.0.0"
   flutter: ">=1.12.13+hotfix.5"

packages/battery/battery/pubspec.yaml

@@ -2,7 +2,7 @@ name: battery
 description: Flutter plugin for accessing information about the battery state
   (full, charging, discharging) on Android and iOS.
 homepage: https://github.com/flutter/plugins/tree/master/packages/battery/battery
-version: 2.0.0-nullsafety
+version: 2.0.0
 
 flutter:
   plugin:
@@ -16,18 +16,18 @@ flutter:
 dependencies:
   flutter:
     sdk: flutter
-  meta: ^1.3.0-nullsafety
-  battery_platform_interface: ^2.0.0-nullsafety
+  meta: ^1.3.0
+  battery_platform_interface: ^2.0.0
 
 dev_dependencies:
-  mockito: ^5.0.0-nullsafety.0
   flutter_test:
     sdk: flutter
-  plugin_platform_interface: ^1.1.0-nullsafety
+  plugin_platform_interface: ">=1.0.0 <3.0.0"
   integration_test:
     path: ../../integration_test
-  pedantic: ^1.10.0-nullsafety
+  pedantic: ^1.10.0
+  test: ^1.16.3
 
 environment:
-  sdk: ">=2.12.0-0 <3.0.0"
+  sdk: ">=2.12.0-259.9.beta <3.0.0"
   flutter: ">=1.12.13+hotfix.5"

packages/battery/battery/test/battery_test.dart

@@ -4,11 +4,11 @@
 
 import 'dart:async';
 
+import 'package:battery/battery.dart';
 import 'package:battery_platform_interface/battery_platform_interface.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:plugin_platform_interface/plugin_platform_interface.dart';
-import 'package:battery/battery.dart';
-import 'package:mockito/mockito.dart';
+import 'package:test/fake.dart';
 
 void main() {
   group('battery', () {
@@ -30,7 +30,7 @@ void main() {
   });
 }
 
-class MockBatteryPlatform extends Mock
+class MockBatteryPlatform extends Fake
     with MockPlatformInterfaceMixin
     implements BatteryPlatform {
   Future<int> batteryLevel() async {