Directory tree indent guides in File Explorer

It's hard to navigate through project with complex directory structure.

Much better to look at something like this:

```
├─ app
|  └─ main.js
├─ src
|  ├─ main.ts
|  └─ tsconfig.json
└─ package.json
```

Instead of this:

```
  app
    main.js
  src
    main.ts
    tsconfig.json
  package.json
```
