Variable/Attribute alias

I always use this workaround as an alias for a variable.

```
class A {
B b;
}

class B {
bool isLoading;
}

class C {
A a;
bool get isLoading => a.b.isLoading;
set isLoading(bool v) {
a.b.isLoading = v;
}
}
```

Could add a new keyword like below to make it easily?

```
class C {
A a;
gset isLoading = a.b.isLoading;
}
```

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Dart Version: 2.2.0
OS: Windows
Browser: Chrome