Add option to indicate bundle encoding

Summary: public

To improve cold start performance we want to be able to avoid decoding the bundle at all. To make that happen we need to be able to generate a bundle encoded on `ucs2`. This diff adds support for indicating the encoding the Packager should use for bundling.

Reviewed By: davidaurelio

Differential Revision: D2582365

fb-gh-sync-id: 905384272a668910c57a1a2ca6d1b723c39233f8

local-cli/bundle/bundleCommandLineArgs.js

@@ -32,6 +32,11 @@ module.exports = [
     description: 'File name where to store the resulting bundle, ex. /tmp/groups.bundle',
     type: 'string',
     required: true,
+  }, {
+    command: 'bundle-encoding',
+    description: 'Encoding the bundle should be written in (https://nodejs.org/api/buffer.html#buffer_buffer).',
+    type: 'string',
+    default: 'utf8',
   }, {
     command: 'sourcemap-output',
     description: 'File name where to store the sourcemap file for resulting bundle, ex. /tmp/groups.map',