Debugging in VSCode

Summary:
This diff enables debugging in VSCode. Debugging works for both Flipper core and plugin code. To start debugging:
1. yarn start
2. Go to "Debug and Run" tab in VSCode, select task "Attach to Running Renderer" and launch it (or just press F5).
{F227135377}
3. Debugger will be attached and all the breakpoints set in VSCode will be hit.

Reviewed By: passy

Differential Revision: D19578566

fbshipit-source-id: 609766471ad196a2ee8d4086ddb84b7af4ef05ef

.vscode/launch.json

@@ -6,7 +6,8 @@
       "type": "chrome",
       "request": "attach",
       "port": 9222,
-      "webRoot": "${workspaceRoot}"
+      "webRoot": "/",
+      "url": "http://localhost:3000/index.dev.html"
     },
     {
       "type": "node",