Move desktop-related code to "desktop" subfolder (#872)

Summary:
Pull Request resolved: https://github.com/facebook/flipper/pull/872
Move all the JS code related to desktop app to "desktop" subfolder.

The structure of "desktop" folder:
- `src` - JS code of Flipper desktop app executing in Electron Renderer (Chrome) process. This folder also contains all the Flipper plugins in subfolder "src/plugins".
- `static` - JS code of Flipper desktop app bootstrapping executing in Electron Main (Node.js) process
- `pkg` - Flipper packaging lib and CLI tool
- `doctor` - Flipper diagnostics lib and CLI tool
- `scripts` - Build scripts for Flipper desktop app
- `headless` - Headless version of Flipper app
- `headless-tests` - Integration tests running agains Flipper headless version

Reviewed By: passy

Differential Revision: D20249304

fbshipit-source-id: 9a51c63b51b92b758a02fc8ebf7d3d116770efe9

desktop/scripts/metro-transform.js

@@ -0,0 +1,65 @@
+/**
+ * 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
+ */
+
+const generate = require('babel-generator').default;
+const babylon = require('babylon');
+const babel = require('babel-core');
+const metro = require('metro');
+
+exports.transform = function({
+  filename,
+  options,
+  src,
+  plugins: defaultPlugins,
+}) {
+  const presets = [];
+
+  let ast = babylon.parse(src, {
+    filename,
+    plugins: ['jsx', 'flow', 'classProperties', 'objectRestSpread'],
+    sourceType: filename.includes('node_modules') ? 'script' : 'module',
+  });
+
+  // run babel
+  const plugins = [
+    ...defaultPlugins,
+    require('./babel-plugins/electron-requires.js'),
+    require('./babel-plugins/dynamic-requires.js'),
+  ];
+  if (!filename.includes('node_modules')) {
+    plugins.unshift(require('babel-plugin-transform-es2015-modules-commonjs'));
+  }
+  ast = babel.transformFromAst(ast, src, {
+    babelrc: !filename.includes('node_modules'),
+    code: false,
+    comments: false,
+    compact: false,
+    filename,
+    plugins,
+    presets,
+    sourceMaps: true,
+  }).ast;
+
+  const result = generate(
+    ast,
+    {
+      filename,
+      sourceFileName: filename,
+      sourceMaps: true,
+    },
+    src,
+  );
+
+  return {
+    ast,
+    code: result.code,
+    filename,
+    map: result.rawMappings.map(metro.sourceMaps.compactMapping),
+  };
+};