(Java Parity) Bosses should not travel through portals

In Java, bosses cannot travel through portals, making it easy to farm withers under the end exit portal in Java. In Bedrock, bosses can travel through portals.

Example:

• In Bedrock, it is hard to farm withers under the end exit portal, possibly resulting in withers at Overworld spawn, because the wither travelled through the portal.

Bosses on Bedrock should not travel through portals.