Remove uses of ImmutableOpen*Map

[rjernst]

After #84735, hppc usage in Elasticsearch is now isolated to ImmutableOpenMap and ImmutableOpenIntMap. This is a meta issue delineating the remaining uses of those classes that need to be removed.

• ImmutableOpenIntMap (Remove ImmutableOpenIntMap #86447)
  • server
    • o.e.Version (Remove ImmutableOpen*Map from Version #86245)
    • o.e.action.admin.indices.shards (Convert IndicesShardStoreResponse to use Map #86281)
    • o.e.cluster.metadata.IndexMetadata (Use HashMap for IndexMetadata.inSyncAllocationIds #86403)
    • o.e.cluster.routing.IndexRoutingTable (Remove use of ImmutableOpenIntMap in IndexRoutingTable #86368)
  • server tests
    • o.e.action.admin.indices.shards (Convert IndicesShardStoreResponse to use Map #86281)
    • o.e.cluster.health (Remove ImmutableOpenIntMap from ClusterStateHealthTests #86306)
  • server integ tests
    • o.e.action.admin.indices.shards (Convert IndicesShardStoreResponse to use Map #86281)
    • o.e.cluster.routing (Remove use of ImmutableOpenIntMap in IndexRoutingTable #86368)
• ImmutableOpenMap exposed by public methods
  • o.e.action.admin.indices (Use Map in indices responses #87292)
  • o.e.cluster.ClusterState (Convert cluster state "customs" to Map #87265)
  • other o.e.cluster (Convert o.e.cluster to use Map in public methods #87168)
• general ImmutableOpenMap usages
  • server tests (Remove ImmutableOpenMap from some server tests #89864, Further changes to remove ImmutableOpenMap from server tests #89939)
  • server integ tests
  • test framework
  • xpack core
  • data streams
  • autoscaling
  • ccr
  • deprecation
  • enrich
  • ilm tests
  • ML
  • QL
  • rollup
  • searchable snapshots
  • security
  • node shutdown
  • transforms
  • watcher

[elasticmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[dakrone]

@rjernst do we still plan to keep some (most?) of these as immutable maps, or are we converting to mutable HashMap-like maps for these?

[rjernst]

Yes I think they can and should remain immutable, just immutable Map instances with Map.of or Map.copyOf.