Add Blackstone Overworld ores for improved Terralith cave gen

[joobert]

What is your idea about?

Terralith's overworld gen features blackstone in place of deepslate throughout many caves. However, the ores that generated here (Iron, coal, diamond, etc.) are still deepslate. Blackstone ores would really help tie the world together!

[elhertz]

+1
I also would like this feature to be added but for a different reason.
I tweaked the overworld noise settings to make a multilayered world and my deepest layer is made of blackstone.
My andesite, diorite, and granite layers work fine with the mod but the blackstone one generates normal stone ores instead of blackstone ones.