Create Auto Properties in Dart

[C# has auto properties](https://stackoverflow.com/a/6001941/1227166) which make creating public getters and private setters really easy, like `public string Example { get; private set; }`

I would like to suggest that we have something similar in Dart, like this:

```dart
int get _set count = 5;
```

This code would be equivalent to what we have to do now:

```dart
int _count = 5;
int get count => _count;
```