api: Add routes registerFcmToken, registerApnsToken

This code is so trivial that I'm torn on whether the tests are
actually useful; they feel a lot like just repeating the implementation.
But they were easy to write.

lib/api/route/notifications.dart

@@ -0,0 +1,30 @@
+
+import '../core.dart';
+
+// This endpoint is undocumented.  Compare zulip-mobile:
+//   https://github.com/zulip/zulip-mobile/blob/86d94fa89/src/api/notifications/savePushToken.js
+// and see the server implementation:
+//   https://github.com/zulip/zulip/blob/34ceafadd/zproject/urls.py#L383
+//   https://github.com/zulip/zulip/blob/34ceafadd/zerver/views/push_notifications.py#L47
+Future<void> registerFcmToken(ApiConnection connection, {
+  required String token,
+}) {
+  return connection.post('registerFcmToken', (_) {}, 'users/me/android_gcm_reg_id', {
+    'token': RawParameter(token),
+  });
+}
+
+// This endpoint is undocumented.  Compare zulip-mobile:
+//   https://github.com/zulip/zulip-mobile/blob/86d94fa89/src/api/notifications/savePushToken.js
+// and see the server implementation:
+//   https://github.com/zulip/zulip/blob/34ceafadd/zproject/urls.py#L378-L381
+//   https://github.com/zulip/zulip/blob/34ceafadd/zerver/views/push_notifications.py#L34
+Future<void> registerApnsToken(ApiConnection connection, {
+  required String token,
+  String? appid,
+}) {
+  return connection.post('registerApnsToken', (_) {}, 'users/me/apns_device_token', {
+    'token': RawParameter(token),
+    if (appid != null) 'appid': RawParameter(appid),
+  });
+}

test/api/route/notifications_test.dart

@@ -0,0 +1,59 @@
+import 'package:checks/checks.dart';
+import 'package:http/http.dart' as http;
+import 'package:test/scaffolding.dart';
+import 'package:zulip/api/route/notifications.dart';
+
+import '../../stdlib_checks.dart';
+import '../fake_api.dart';
+
+void main() {
+  group('registerFcmToken', () {
+    Future<void> checkRegisterFcmToken(FakeApiConnection connection, {
+      required String token,
+    }) async {
+      connection.prepare(json: {});
+      await registerFcmToken(connection, token: token);
+      check(connection.lastRequest).isA<http.Request>()
+        ..method.equals('POST')
+        ..url.path.equals('/api/v1/users/me/android_gcm_reg_id')
+        ..bodyFields.deepEquals({
+          'token': token,
+        });
+    }
+
+    test('smoke', () {
+      return FakeApiConnection.with_((connection) async {
+        await checkRegisterFcmToken(connection, token: 'asdf');
+      });
+    });
+  });
+
+  group('registerApnsToken', () {
+    Future<void> checkRegisterApnsToken(FakeApiConnection connection, {
+      required String token,
+      required String? appid,
+    }) async {
+      connection.prepare(json: {});
+      await registerApnsToken(connection, token: token, appid: appid);
+      check(connection.lastRequest).isA<http.Request>()
+        ..method.equals('POST')
+        ..url.path.equals('/api/v1/users/me/apns_device_token')
+        ..bodyFields.deepEquals({
+          'token': token,
+          if (appid != null) 'appid': appid,
+        });
+    }
+
+    test('no appid', () {
+      return FakeApiConnection.with_((connection) async {
+        await checkRegisterApnsToken(connection, token: 'asdf', appid: null);
+      });
+    });
+
+    test('with appid', () {
+      return FakeApiConnection.with_((connection) async {
+        await checkRegisterApnsToken(connection, token: 'asdf', appid: 'qwer');
+      });
+    });
+  });
+}