For blocks, we now use 'block-item state' and 'block-only state', which should be much clearer for people implementing custom stuff.
'block-item state', as the name suggests, sticks to the item when the block is acquired as an item.
'block-only state' applies only to the block and is discarded when the block is acquired as an item.
'type data' for items was also renamed, since 'type' is too ambiguous to be anything but super confusing.
originally I introduced this to make it easier to implement the various APIs addPattern removePattern etc, but those were later removed in favour of simple getPatterns() and setPatterns(), allowing plugin developers to use ext-ds APIs to manipulate patterns.
However, ds poses a number of headaches because of mutability combined with by-ref semantics, which make it a pain to use these on the APIs because we can't guarantee that they won't be modified.
As much as arrays suck, they have two significant advantages over ext-ds: 1) they have copy-on-write semantics, and 2) they support PHP 8.0 without any extra work from me.
