Expose getLastCommittedSegmentInfos in Engine (#97978)

As Engine.getLastCommittedSegmentInfos() is effectively immutable, it is acceptable to expose.

server/src/main/java/org/elasticsearch/index/engine/Engine.java

@@ -146,7 +146,7 @@ public abstract class Engine implements Closeable {
         return engineConfig;
     }
 
-    protected abstract SegmentInfos getLastCommittedSegmentInfos();
+    public abstract SegmentInfos getLastCommittedSegmentInfos();
 
     public MergeStats getMergeStats() {
         return new MergeStats();

server/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -2478,7 +2478,7 @@ public class InternalEngine extends Engine {
     }
 
     @Override
-    protected SegmentInfos getLastCommittedSegmentInfos() {
+    public SegmentInfos getLastCommittedSegmentInfos() {
         return lastCommittedSegmentInfos;
     }
 

server/src/main/java/org/elasticsearch/index/engine/ReadOnlyEngine.java

@@ -287,7 +287,7 @@ public class ReadOnlyEngine extends Engine {
     }
 
     @Override
-    protected SegmentInfos getLastCommittedSegmentInfos() {
+    public SegmentInfos getLastCommittedSegmentInfos() {
         return lastCommittedSegmentInfos;
     }