Add DynamicFeature system channel (#71879)

packages/flutter/lib/src/services/system_channels.dart

@@ -318,4 +318,30 @@ class SystemChannels {
     'flutter/restoration',
     StandardMethodCodec(),
   );
+
+  /// A [MethodChannel] for installing and managing dynamic features.
+  ///
+  /// The following outgoing methods are defined for this channel (invoked using
+  /// [OptionalMethodChannel.invokeMethod]):
+  ///
+  ///  * `installDynamicFeature`: Requests that a dynamic feature identified by
+  ///    the provided loadingUnitId or moduleName be downloaded and installed.
+  ///    Providing a loadingUnitId with null moduleName will install a dynamic
+  ///    feature module that includes the desired loading unit. If a moduleName
+  ///    is provided, then the dynamic feature with the moduleName will be installed.
+  ///    This method returns a future that will not be completed until the
+  ///    feature is fully installed and ready to use. When an error occurs, the
+  ///    future will complete an error. Calling `loadLibrary()` on a deferred
+  ///    imported library is equivalent to calling this method with a
+  ///    loadingUnitId and null moduleName.
+  ///  * `getDynamicFeatureInstallState`: Gets the current installation state of
+  ///    the dynamic feature identified by the loadingUnitId or moduleName.
+  ///    This method returns a string that represents the state. Depending on
+  ///    the implementation, this string may vary, but the default Google Play
+  ///    Store implementation beings in the "Requested" state before transitioning
+  ///    into the "Downloading" and finally the "Installed" state.
+  static const MethodChannel dynamicfeature = OptionalMethodChannel(
+    'flutter/dynamicfeature',
+    StandardMethodCodec(),
+  );
 }