Expose position of textarea

# Description
Comparing with [firenvim](https://github.com/glacambre/firenvim), I prefer GhostText, which is not conflicted my shortcuts in chromium and doesn't slow me down in neovim.

I have tried GhostText with [raghur/vim-ghost](https://github.com/raghur/vim-ghost). I wanna make the position of nvim cover the textarea so I need the position of textarea. After enabling the log, the position of the textarea isn't passed to websocket server.

```log
recd on websocket: ('127.0.0.1', 53718) message:
{"text":"","selections":[{"start":0,"end":0}],"title":"xxxxxxxxx","url":"github.com","syntax":""}
```