E.g. in stone where it had already been spawned in maps prior to this change,
in structures made with the old block, etc.
Mese ore (of a sort), as default:stone_with_mese, is generated now instead of
default:mese (which is not generated at all now).
The new default:mese_block is substituted in place of default:mese by way of an
alias.
Crystals still come from Mese Crystals in Stone, while digging buried Mese
Blocks returns exactly those (the same as can be crafted from 9 crystals). If
necessary, they can be split up into Mese Crystals again via the existing
crafting recipe.
This alters the value of the various Mese items a little, but avoids breaking
old structures that were made of mese.
The original default:mese, if needed, can be obtained by crafting two Mese
Crystals, which yields two of the old Mese object. Two of these can be crafted
back into two Crystals if needed.
