AssignableReplica breaking hashCode and equals contracts

[qqu0127]

Describe the bug

In https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/controller/rebalancer/waged/model/AssignableReplica.java#L127, it overrides equals, but not hashCode. This is violating the Object.hashCode() contract and breaking lots of assumption, especially with hash-based collection.

What makes it even more awkward is the code building on top of this anti-pattern,

helix/helix-core/src/main/java/org/apache/helix/controller/rebalancer/waged/model/ClusterModelProvider.java

Line 450 in 0274d5a

private static Map<String, Set<AssignableReplica>> getAllAssignableReplicas(

, it could contain "duplicated" elements (two standby replicas of a partition). It really should be a list to begin with.

Expected behavior

We should fix the hashCode and change to use List instead of Set to store values with duplication.

Additional context

Add any other context about the problem here.