update js-client api (migrate to TS)

Summary:
JS/TS api:
- migrate to TS
- some refactoring (get rid of bridge, make client abstract)

Implementation isn't full yet, things to be implemented:
- let plugins connect on init command from Flipper
- implement Responder

Further plans:
- make fully compatible with react-native api without breaking changes

Reviewed By: mweststrate

Differential Revision: D21839377

fbshipit-source-id: 9e9fe4ad01632f958b59eb255c703c6cbc5fafe2

flipper-js-client-sdk/src/example.ts

@@ -0,0 +1,50 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {FlipperClient, AbstractFlipperPlugin} from './api';
+import {newWebviewClient} from './webviewImpl';
+
+class SeaMammalPlugin extends AbstractFlipperPlugin {
+  getId(): string {
+    return 'sea-mammals';
+  }
+
+  runInBackground(): boolean {
+    return true;
+  }
+
+  newRow(row: {id: string, url: string, title: string}) {
+    this.connection?.send("newRow", row)
+}
+
+}
+
+class FlipperManager {
+  flipperClient: FlipperClient;
+  seaMammalPlugin: SeaMammalPlugin;
+
+  constructor() {
+    this.flipperClient = newWebviewClient();
+    this.seaMammalPlugin = new SeaMammalPlugin();
+    this.flipperClient.addPlugin(this.seaMammalPlugin);
+    this.flipperClient.start('Example JS App');
+  }
+}
+
+let flipperManager: FlipperManager | undefined;
+
+export function init() {
+  if (!flipperManager) {
+    flipperManager = new FlipperManager();
+  }
+}
+
+export function flipper(): FlipperManager | undefined {
+  return flipperManager;
+}