Initialise flipper-ui-browser with socket connection

Summary:
This diff sets up the socket connection between flipper-browser and flipper-server, and verifies that the initial UI initialisation work (e.g. `get-config` command works). The initial RenderHost is initialised as well based on the config and browser APIs.

Note that flipper-ui-core itself isn't started yet, as that has still a plethora of node imports, so Metro will correctly refuse to bundle

Not in this diff
* remove Node usage from flipper-ui-core
* implement all RenderHost APIs

Reviewed By: aigoncharov

Differential Revision: D32644074

fbshipit-source-id: 2c8065caf0191771a3867b69a431ca50eeb7a5a3

desktop/flipper-ui-browser/src/global.ts

@@ -0,0 +1,25 @@
+/**
+ * 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 {RenderHost} from 'flipper-ui-core';
+
+declare global {
+  interface Window {
+    flipperConfig: {
+      theme: 'light' | 'dark' | 'system';
+      entryPoint: string;
+      debug: boolean;
+    };
+
+    FlipperRenderHostInstance: RenderHost;
+
+    flipperShowError?(error: string): void;
+    flipperHideError?(): void;
+  }
+}