Adding components for binding the C++ libraries with flutter app

- Branch class Listener from google3/location/nearby/cpp/sharing/clients/dart/platform/lib/listener.dart for further use of listening the change from notification controller.
- Create Device Metadata to store the device information relating to UI showing.
- Create binding class to bind C++ libraries to dart language.

PiperOrigin-RevId: 540644654

fastpair/dart/binding/lib/bindings.dart

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+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import 'dart:ffi';
+
+import 'ffi_types.dart';
+
+class FastpairBinding {
+  static final _lib = DynamicLibrary.open('fastpair_dart.dll');
+
+  late final InitMediatorDartType initMediator = _lib
+      .lookup<NativeFunction<InitMediatorType>>(
+        'InitMediatorDart',
+      )
+      .asFunction();
+
+  late final CloseMediatorDartType closeMediator = _lib
+      .lookup<NativeFunction<CloseMediatorType>>('CloseMediator')
+      .asFunction();
+
+  late final StartFastPairScanningDartType startFastPairScanning = _lib
+      .lookup<NativeFunction<StartFastPairScanningType>>('StartScanDart')
+      .asFunction();
+
+  late final InitializeApiDartType initializeApi = _lib
+      .lookup<NativeFunction<InitializeApiType>>('Dart_InitializeApiDL')
+      .asFunction();
+
+  late final AddNotificationControllerObserverDartType
+      addNotificationControllerObserver = _lib
+          .lookup<NativeFunction<AddNotificationControllerObserverType>>(
+              'AddNotificationControllerObserverDart')
+          .asFunction();
+
+  late final RemoveNotificationControllerObserverDartType
+      removeNotificationControllerObserver = _lib
+          .lookup<NativeFunction<RemoveNotificationControllerObserverType>>(
+              'RemoveNotificationControllerObserverDart')
+          .asFunction();
+
+  late final DiscoveryClickedDartType discoveryClicked = _lib
+      .lookup<NativeFunction<DiscoveryClickedType>>('DiscoveryClickedDart')
+      .asFunction();
+}

fastpair/dart/binding/lib/device_metadata.dart

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+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Detail information of a observed device. Compared to the device information
+// get from GetObservedDeviceResponse, this class only store the device
+// information that is related to UI showing.
+class DeviceMetadata {
+  String id;
+  String name;
+  String imageUrl;
+
+  DeviceMetadata({
+    required this.id,
+    required this.name,
+    required this.imageUrl,
+  });
+
+  factory DeviceMetadata.fromJson(dynamic data) {
+    return DeviceMetadata(
+      id: data['id'],
+      name: data['name'] == '' ? null : data['name'],
+      imageUrl: data['imageUrl'] == '' ? null : data['imageUrl'],
+    );
+  }
+}

fastpair/dart/binding/lib/ffi_types.dart

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+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import 'dart:ffi';
+
+import 'device_metadata.dart';
+
+typedef InitMediatorType = Pointer<Uint64> Function();
+typedef InitMediatorDartType = Pointer<Uint64> Function();
+
+typedef CloseMediatorType = Void Function(Pointer<Uint64> /*service*/);
+typedef CloseMediatorDartType = void Function(Pointer<Uint64> /*service*/);
+
+typedef StartFastPairScanningType = Void Function(Pointer<Uint64> /*service*/);
+typedef StartFastPairScanningDartType = void Function(
+    Pointer<Uint64> /*service*/);
+
+typedef AddNotificationControllerObserverType = Void Function(
+  Pointer<Uint64> /*service*/,
+  Int64 /* callback*/,
+);
+typedef AddNotificationControllerObserverDartType = void Function(
+  Pointer<Uint64> /*service*/,
+  int /* callback*/,
+);
+
+typedef RemoveNotificationControllerObserverType = Void Function(
+  Pointer<Uint64> /*service*/,
+  Int64 /* callback*/,
+);
+typedef RemoveNotificationControllerObserverDartType = void Function(
+  Pointer<Uint64> /*service*/,
+  int /* callback*/,
+);
+
+typedef DiscoveryClickedType = Void Function(
+  Pointer<Uint64> /*service*/,
+  Int64 /* callback*/,
+);
+typedef DiscoveryClickedDartType = void Function(
+  Pointer<Uint64> /*service*/,
+  int /* callback*/,
+);
+
+typedef InitializeApiType = IntPtr Function(Pointer<Void>);
+typedef InitializeApiDartType = int Function(Pointer<Void>);
+
+//callback type
+typedef OnMetadataChanged = void Function({
+  required List<DeviceMetadata> deviceMetadata,
+});

fastpair/dart/binding/lib/listener.dart

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+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import 'dart:ffi';
+import 'dart:isolate';
+
+import 'package:mobile.flutter.contrib.disposable/disposable.dart';
+
+/// A convenience class for listening to a [ReceivePort].
+///
+/// This can be used to listen to ongoing updates from the c++ layer.
+class Listener with AutoDisposerMixin {
+  Listener() {
+    autoDisposeCustom(_port.close);
+    autoDisposeCustom(_subscription.cancel);
+  }
+
+  final _port = ReceivePort();
+  late final _subscription = _port.listen(null);
+
+  int get port => _port.sendPort.nativePort;
+
+  void onData(void Function(dynamic data)? handleData) =>
+      _subscription.onData(handleData);
+}