[flutter_local_notifications] updated presentSound and defaultPresent…

…Sound API docs around background app behaviour (#2112)

* added more details on background sound behaviour to presentSound and defaultPresentSound

* added changelog entry

flutter_local_notifications/CHANGELOG.md

@@ -6,6 +6,7 @@
 * [Android] bumped Java desugaring dependency and updated readme accordingly to also mention Gradle version that is used by plugin
 * [Android] fixed issue an issue similar to [2033](https://github.com/MaikuB/flutter_local_notifications/issues/2033) that was addressed in 15.0.1 where notifications on scheduled using older version of the plugin via the `periodicallyShow()` method would fail to have the next subsequent ones scheduled. This issue started occuring in 14.0 where support for inexact notifications was added using the `ScheduleMode` enum that was added and resulted in the deprecation of `androidAllowWhileIdle`. A mechanism was added to help "migrate" old notifications that had `androidAllowWhileIdle` specified but didn't account for how there are recurring notifications that were scheduled using older versions of the plugin prior to `androidAllowWhile` being added. This was also released as part of the 15.1.1 and 14.1.3 hotfix releases
 * [Android] fixed issue [2106](https://github.com/MaikuB/flutter_local_notifications/issues/2106) where calling `getNotificationChannels()` reports the wrong importance level or result in an exception if the importance level was unspecified. This was also released as part of the 15.1.2 and 14.1.4 hotfix releases
+* [iOS][macOS] addresses issue [2097](https://github.com/MaikuB/flutter_local_notifications/issues/2097) by updating API docs for the `presentSound` and `defaultPresentSound` properties that belong to the `DarwinNotificationDetails` and `DarwinInitializationSettings` classes respectively to clarify the background behaviour and how have a sound play even when app is the background yet these properties are set to false
 * Updated example app so that the Android side specifies minimum SDK version version that aligns with what's specified by the Flutter SDK
 * Fixed Dart API docs for `DarwinNotificationDetails` class where `this This` was being repeated. Thanks to the PR from [Adrian Jagielak](https://github.com/adrianjagielak)
 * Fixed example code shown at the "Handling notifications whilst the app is in the foreground" section of the readme. Thanks to the PR from [Tinh Huynh](https://github.com/TinhHuynh)

flutter_local_notifications/lib/src/platform_specifics/darwin/initialization_settings.dart

@@ -76,6 +76,16 @@ class DarwinInitializationSettings {
   ///
   /// Default value is true.
   ///
+  /// If this is set to false to indicate that the notification shouldn't play
+  /// a sound in the foreground then note that for consistency, the notification
+  /// won't play a sound when the app is in the background. If the intention in
+  /// this scenario is to have the app also play the default notification sound
+  /// whilst the app is in the background as well, then the
+  /// [DarwinNotificationDetails.sound] should be set to an arbitrary value
+  /// (e.g. empty string) that doesn't match a custom sound file. This way the
+  /// platform fails to find a custom sound file to fallback to the default
+  /// notification sound.
+  ///
   /// On iOS, this property is only applicable to iOS 10 or newer.
   /// On macOS, this property is only applicable to macOS 10.14 or newer.
   final bool defaultPresentSound;

flutter_local_notifications/lib/src/platform_specifics/darwin/notification_details.dart

@@ -41,6 +41,15 @@ class DarwinNotificationDetails {
   /// When this is set to `null`, it will use the default setting given
   /// to [DarwinInitializationSettings.defaultPresentSound].
   ///
+  /// If this is set to false to indicate that the notification shouldn't play
+  /// a sound in the foreground then note that for consistency, the notification
+  /// won't play a sound when the app is in the background. If the intention in
+  /// this scenario is to have the app also play the default notification sound
+  /// whilst the app is in the background as well, then the [sound] should be
+  /// set to an arbitrary value (e.g. empty string) that doesn't match a custom
+  /// sound file. This way the platform fails to find a custom sound file to
+  /// fallback to the default notification sound.
+  ///
   /// This property is only applicable to iOS 10 or newer.
   final bool? presentSound;