Grouping by folder inside project group

**Is your feature request related to a problem? Please describe.**
not a problem, but improvement

**Describe the solution you'd like**
Grouping by folder inside project group.

**Describe alternatives you've considered**
for example:

```
// 🌎 Project imports:

../aaa/bbb/foo.dart
../aaa/bbb/bar.dart

../aaa/ccc/ttt.dart
../aaa/ccc/eee.dart
../aaa/ccc/fff.dart

../zzz/ppp.dart
```