Enable the deepening when we update to 1.18

[SengornLeopard]

In 1.18 there will be a setting during the update process which will replace bedrock with deepslate, and add 64 blocks of depth to older chunks.

This of course MUST be selected.

Choosing not to do this would not only be morally heinous, but a blatantly incorrect decision.

Anyone who opposes doing this is either a liar who truly wants to, or a fool who does not yet know they want to.