Expose APIs needed by flush during translog replay (elastic#132960)

Author: lkts

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

@@ -620,6 +620,10 @@ public void skipTranslogRecovery() {
         pendingTranslogRecovery.set(false); // we are good - now we can commit
     }
 
+    protected boolean pendingTranslogRecovery() {
+        return pendingTranslogRecovery.get();
+    }
+
     private void recoverFromTranslogInternal(
         TranslogRecoveryRunner translogRecoveryRunner,
         long recoverUpToSeqNo,
@@ -3133,7 +3137,7 @@ protected Map<String, String> getCommitExtraUserData(final long localCheckpoint)
         return Collections.emptyMap();
     }
 
-    final void ensureCanFlush() {
+    protected void ensureCanFlush() {
         // translog recovery happens after the engine is fully constructed.
         // If we are in this stage we have to prevent flushes from this
         // engine otherwise we might loose documents if the flush succeeds