this switches from a 'can be supported by' concept to a 'can stay at this position' paradigm, which requires way less boilerplate code.
there may be further improvements we can make from here, such as adding traits, but this is a good first step.
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.
This was first attempted in f64dc01bd1, but reverted, since I hadn't considered how to handle stripping state data from blocks.
This removes the abusable API RuntimeBlockStateRegistry::fromTypeId() and related methods. These were only used to allow ItemBlocks to magically start referencing other blocks if the blocks were overridden by a plugin, but this was never a well-supported use-case anyway.
Instead of relying on RuntimeBlockStateRegistry, we remember the state that the block had during its constructor, and use that to normalize the non-item properties for asItem().
closes#5609
