Add routing changes API to RoutingAllocation (#19992)

Adds a class that records changes made to RoutingAllocation, so that at the end of the allocation round other values can be more easily derived based on these changes. Most notably, it:

- replaces the explicit boolean flag that is passed around everywhere to denote changes to the routing table. The boolean flag is automatically updated now when changes actually occur, preventing issues where it got out of sync with actual changes to the routing table.
- records actual changes made to RoutingNodes so that primary term and in-sync allocation ids, which are part of index metadata, can be efficiently updated just by looking at the shards that were actually changed.

1 files changed, 2 insertions, 2 deletions

diff --git a/benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/Allocators.java b/benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/Allocators.java
index 97fbda80dc..9b1cfaabf9 100644
--- a/benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/Allocators.java
+++ b/benchmarks/src/main/java/org/elasticsearch/benchmark/routing/allocation/Allocators.java
@@ -60,8 +60,8 @@ public final class Allocators {
         }
 
         @Override
-        public boolean allocateUnassigned(RoutingAllocation allocation) {
-            return false;
+        public void allocateUnassigned(RoutingAllocation allocation) {
+            // noop
         }
     }