Allow import and part to have wildcard path to import every lib in specific directory

[SPiercer]

i was messing around and had been using part of imports and my main part lib has a massive amount of parts

part 'route/a.dart';
part 'route/b.dart';
part 'route/c.dart';

i guess it would be cool if we could've simply just..

part 'routes/*';

[lrhn]

Duplicate of (at least) #1709

Same argument against: It's fragile. Even if it was part 'routes/*.dart';, it might include something you don't want.
If/when we get part files with imports and further parts, it becomes even less likely that all the files you need are the only files in a directory, and while using globs like part 'banana_concept1_*.dart';, part 'banana_concept2_*.dart'; could work, I hope your editor doesn't write a #banana_concept1_part1.part temporary file.