Implement QFileInfo::birthTime() for Android

Currently, QFileInfo::birthTime() returns null, probably because the Android File API does not expose the information: https://developer.android.com/reference/java/io/File.html

However, as of API Level 26, it is possible to retrieve it as a BasicFileAttribute (source: https://stackoverflow.com/a/48431255/1144539 ):

File file = ...;
BasicFileAttributes attr = Files.readAttributes(file.toPath(), BasicFileAttributes.class);
long createdAt = attr.creationTime().toMillis();