isAvailable method Null safety
Checks if the device is able to show a review dialog.
On Android the Google Play Store must be installed and the device must be running Android 5 Lollipop(API 21) or higher.
IOS devices must be running IOS version 10.3 or higher.
MacOS devices must be running MacOS version 10.14 or higher
Future<bool> isAvailable() => InAppReviewPlatform.instance.isAvailable();