Parity: Bedrock doesn't have "/spreadplayers ... under"

Updated by [Mod] EVGENSYPERPRO

Summary:
"/spreadplayers ... under" was added in Java 1.16, but not in Bedrock.

https://www.minecraft.net/article/nether-update-java

Added an optional argument to specify maximum height. New syntax: spreadplayers <center> [under ]

Steps to reproduce:

1. Enter a world with cheats on
2. Go to chat
3. Type:

   /spreadplayers ... under

Observed results:
There is no /spreadplayers ... under in Bedrock.

Expected results:
It should be there in Bedrock as Java has it in Java Edition 1.16.