Shulkers don't attack back in peaceful difficulty

This bug report is related to MC-227058

Since it was established that hostility between non player mobs is intended in peaceful difficulty I'm making this bug report.

If a shulker gets attacked by a snow golem or other mob, he doesn't fight back in peaceful difficulty. On any other difficulty he defends himself when attacked.
This behaviour is also inconsistent, since a piglin that gets attacked in peaceful difficulty does attack back.