trash method
Deletes uri by moving it to the platform's trash. Answers false when
there is no trash to move it to — the caller then asks before delete:
nothing is unlinked without a way back unless somebody said so.
Implementation
@override
Future<bool> trash(Uri uri) async {
final local = localPathOf(uri);
final moved = await _trash(local);
if (moved) emitChange(uri, TomFileChangeType.deleted);
return moved;
}