Java Edition 21w43a

21w43a is the seventh snapshot for Java Edition 1.18, released on October 27, 2021.

General

 * Old worlds upgrading
 * When generating close to old chunks hew terrain is adjusted to better match the existing terrain at the borders
 * In old chunks, if there is Bedrock at y=0, the column below will be filled with Deepslate
 * Worlds upgraded in this snapshot will permanently have this deepslate.
 * A new Bedrock layer is placed at y=-64