binding: add packageName to the packageInfo class in the binding class

made changes to access packageName from the PackageInfo class.
remove getAppBundleId() from Zulip Binding class
Add packageName variable to PackageInfo class
Fixes zulip#407

Author: Abhisheksainii

lib/model/binding.dart

@@ -303,10 +303,12 @@ class LinuxDeviceInfo implements BaseDeviceInfo {
 class PackageInfo {
   final String version;
   final String buildNumber;
+  final String packageName;
 
   const PackageInfo({
     required this.version,
     required this.buildNumber,
+    required this.packageName,
   });
 }
 
@@ -411,6 +413,7 @@ class LiveZulipBinding extends ZulipBinding {
       _syncPackageInfo = PackageInfo(
         version: info.version,
         buildNumber: info.buildNumber,
+        packageName: info.packageName,
       );
     } catch (e, st) {
       assert(debugLog('Failed to prefetch package info: $e\n$st')); // TODO(log)

test/model/binding.dart

@@ -229,7 +229,7 @@ class TestZulipBinding extends ZulipBinding {
 
   /// The value that `ZulipBinding.instance.packageInfo` should return.
   PackageInfo packageInfoResult = _defaultPackageInfo;
-  static const _defaultPackageInfo = PackageInfo(version: '0.0.1', buildNumber: '1');
+  static const _defaultPackageInfo = PackageInfo(version: '0.0.1', buildNumber: '1', packageName: 'com.zulip.flutter.test');
 
   void _resetPackageInfo() {
     packageInfoResult = _defaultPackageInfo;
@@ -380,6 +380,7 @@ class TestZulipBinding extends ZulipBinding {
   Future<void> toggleWakelock({required bool enable}) async {
     _wakelockEnabled = enable;
   }
+
 }
 
 class FakeFirebaseMessaging extends Fake implements FirebaseMessaging {