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/static/transforms/import-react.js

@@ -0,0 +1,53 @@
+/**
+ * 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
+ */
+
+module.exports = function(babel) {
+  const t = babel.types;
+
+  return {
+    name: 'infinity-import-react',
+    visitor: {
+      Program: {
+        exit(path, state) {
+          if (state.get('NEEDS_REACT')) {
+            path.unshiftContainer('body', [
+              t.variableDeclaration('var', [
+                t.variableDeclarator(
+                  t.identifier('React'),
+                  t.callExpression(t.identifier('require'), [
+                    t.stringLiteral('react'),
+                  ]),
+                ),
+              ]),
+            ]);
+          }
+        },
+      },
+
+      ReferencedIdentifier(path, state) {
+        // mark react as needing to be imported
+        if (path.node.name === 'React' && !path.scope.getBinding('React')) {
+          state.set('NEEDS_REACT', true);
+        }
+
+        // replace Buffer with require('buffer')
+        if (path.node.name === 'Buffer' && !path.scope.getBinding('Buffer')) {
+          path.replaceWith(
+            t.memberExpression(
+              t.callExpression(t.identifier('require'), [
+                t.stringLiteral('buffer'),
+              ]),
+              t.identifier('Buffer'),
+            ),
+          );
+        }
+      },
+    },
+  };
+};