Use internal searcher for all indexing related operations in the engine

The changes introduced in #26972 missed two places where an internal searcher should be used.

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

@@ -525,7 +525,7 @@ public class InternalEngine extends Engine {
         } else {
             // load from index
             assert incrementIndexVersionLookup();
-            try (Searcher searcher = acquireSearcher("load_seq_no")) {
+            try (Searcher searcher = acquireSearcher("load_seq_no", SearcherScope.INTERNAL)) {
                 DocIdAndSeqNo docAndSeqNo = VersionsAndSeqNoResolver.loadDocIdAndSeqNo(searcher.reader(), op.uid());
                 if (docAndSeqNo == null) {
                     status = OpVsLuceneDocStatus.LUCENE_DOC_NOT_FOUND;
@@ -952,7 +952,7 @@ public class InternalEngine extends Engine {
                 throw new AssertionError("doc [" + index.type() + "][" + index.id() + "] exists in version map (version " + versionValue + ")");
             }
         } else {
-            try (Searcher searcher = acquireSearcher("assert doc doesn't exist")) {
+            try (Searcher searcher = acquireSearcher("assert doc doesn't exist", SearcherScope.INTERNAL)) {
                 final long docsWithId = searcher.searcher().count(new TermQuery(index.uid()));
                 if (docsWithId > 0) {
                     throw new AssertionError("doc [" + index.type() + "][" + index.id() + "] exists [" + docsWithId + "] times in index");
@@ -1659,7 +1659,9 @@ public class InternalEngine extends Engine {
             assert rwl.isWriteLockedByCurrentThread() || failEngineLock.isHeldByCurrentThread() : "Either the write lock must be held or the engine must be currently be failing itself";
             try {
                 this.versionMap.clear();
-                internalSearcherManager.removeListener(versionMap);
+                if (internalSearcherManager != null) {
+                    internalSearcherManager.removeListener(versionMap);
+                }
                 try {
                     IOUtils.close(externalSearcherManager, internalSearcherManager);
                 } catch (Exception e) {