It looks like BaseSpawner will not run natural spawn finalization
unless the entire data tag only contains the ID.
This only fixes converting old data, we need a fix for already
converted data.
When converting entity/poi data (SimpleRegionStorage),
we need to insert the new data version so that force upgrading
will write the data back with the correct version.
It's important to convert the ItemStack present inside
the text component. The ItemStack nests TEXT_COMPONENT (written
book pages, custom name, ...) which would otherwise not be walked
since we have set a breakpoint at the version and moved the walker
to the next version step.
This fixes item names for hover events inside written book pages
failing to convert to NBT. This issue is also present on DFU.
