Create new file quick fix for enhanced part always uses the main file name

[FMorschel]

Create main.dart:

part 'part.dart';

Then trigger the quick-fix to create the part.dart file.

Inside part.dart:

part of 'main.dart';

part 'inner-part.dart';

Do the same for the new file, it'll give a new error:

Expected this library to be part of 'package:bug/part.dart', not 'package:bug/inner-part.dart'.
Try including a different part, or changing the name of the library in the part's part-of directive.dart[part_of_different_library](https://dart.dev/diagnostics/part_of_different_library)

Because the generated inner-part:

part of 'main.dart';

[bwilkerson]

Not only is the wrong path used in the part of directive, but the diagnostic has the path of the file containing the error rather than the file that is incorrectly referenced.

[FMorschel]

I think the wrong error message has the same root cause as #56541.