Re-enable use of instruments for iOS device lookup (#10838)

This reverts commit b2909a245a607995ce7ec286585cd1f643124f57.

This resubmits the following patches:

1. Use Xcode instruments to list devices (#10801)
Eliminates the dependency on idevice_id from libimobiledevice. Instead,
uses Xcode built-in functionality.

2. Make device discovery asynchronous (#10803)
Migrates DeviceDiscovery.devices and all device-specific lookup to be
asynchronous.

packages/flutter_tools/test/src/mocks.dart

diff --git a/packages/flutter_tools/test/src/mocks.dart b/packages/flutter_tools/test/src/mocks.dart
index 1ac69c9..3cbfdb3 100644
--- a/packages/flutter_tools/test/src/mocks.dart
+++ b/packages/flutter_tools/test/src/mocks.dart
@@ -37,7 +37,7 @@
   MockPollingDeviceDiscovery() : super('mock');
 
   @override
-  List<Device> pollingGetDevices() => _devices;
+  Future<List<Device>> pollingGetDevices() async => _devices;
 
   @override
   bool get supportsPlatform => true;
@@ -52,7 +52,7 @@
   }
 
   @override
-  List<Device> get devices => _devices;
+  Future<List<Device>> get devices async => _devices;
 
   @override
   Stream<Device> get onAdded => _onAddedController.stream;