address false positives in "make late" quick fix

[pq]

Followup from https://dart-review.googlesource.com/c/sdk/+/176900/2..3/pkg/analysis_server/test/src/services/correction/fix/add_late_test.dart#57.

In a.dart:

class C {
  final String s;
}

In b.dart:

import 'a.dart';

void f(C c) {
  c.s = '';
}

The diagnostic will be reported in b.dart but the edit needs to be applied to a.dart (or disallowed).

... different parts would have the same problem as different libraries and should also be tested ...

In a.dart:

part 'b.dart';

class C {
  final String s;
}

In b.dart:

part of 'a.dart';

void f(C c) {
  c.s = '';
}

Again, the diagnostic will be reported in b.dart but the edit needs to be applied to a.dart.

[pq]

I did a a little investigating. The fix is not proposed for parts but is wrongly applied for the second file case.

Failing test added https://dart-review.googlesource.com/c/sdk/+/178661.

[pq]

Fixed w/ https://dart-review.googlesource.com/c/sdk/+/180087.