Pass AbstractType::Ptr, not Declaration*, to accessAttribute()

All but one caller had to look up the declaration only to have it converted

back, so the previous version was pointless anyway.

This allows subscripting of expressions (inc. other subscripts), when the

subscripted type isn't a ListType/IndexedContainer.

BUG: 359912
Differential Revision: https://phabricator.kde.org/D3422