make some method of ManagedLedger public (#5472)

Some of the ManagedLedger methods, such as hasMoreEntries/getPreviousPosition/getNextValidPosition, are protected. This change try to make them public.
These methods are useful when user want to do some advanced operation in Data Processing.

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java

@@ -209,7 +209,7 @@ public class ManagedLedgerImpl implements ManagedLedger, CreateCallback {
     }
 
     // define boundaries for position based seeks and searches
-    enum PositionBound {
+    public enum PositionBound {
         startIncluded, startExcluded
     }
 
@@ -1727,7 +1727,7 @@ public class ManagedLedgerImpl implements ManagedLedger, CreateCallback {
         return mbean;
     }
 
-    boolean hasMoreEntries(PositionImpl position) {
+    public boolean hasMoreEntries(PositionImpl position) {
         PositionImpl lastPos = lastConfirmedEntry;
         boolean result = position.compareTo(lastPos) <= 0;
         if (log.isDebugEnabled()) {
@@ -2625,7 +2625,7 @@ public class ManagedLedgerImpl implements ManagedLedger, CreateCallback {
      *            specifies whether or not to include the start position in calculating the distance
      * @return the new position that is n entries ahead
      */
-    PositionImpl getPositionAfterN(final PositionImpl startPosition, long n, PositionBound startRange) {
+    public PositionImpl getPositionAfterN(final PositionImpl startPosition, long n, PositionBound startRange) {
         long entriesToSkip = n;
         long currentLedgerId;
         long currentEntryId;
@@ -2693,7 +2693,7 @@ public class ManagedLedgerImpl implements ManagedLedger, CreateCallback {
      *            the current position
      * @return the previous position
      */
-    PositionImpl getPreviousPosition(PositionImpl position) {
+    public PositionImpl getPreviousPosition(PositionImpl position) {
         if (position.getEntryId() > 0) {
             return PositionImpl.get(position.getLedgerId(), position.getEntryId() - 1);
         }
@@ -2755,15 +2755,15 @@ public class ManagedLedgerImpl implements ManagedLedger, CreateCallback {
         }
     }
 
-    boolean ledgerExists(long ledgerId) {
+    public boolean ledgerExists(long ledgerId) {
         return ledgers.get(ledgerId) != null;
     }
 
-    Long getNextValidLedger(long ledgerId) {
+    public Long getNextValidLedger(long ledgerId) {
         return ledgers.ceilingKey(ledgerId + 1);
     }
 
-    PositionImpl getNextValidPosition(final PositionImpl position) {
+    public PositionImpl getNextValidPosition(final PositionImpl position) {
         PositionImpl nextPosition = position.getNext();
         while (!isValidPosition(nextPosition)) {
             Long nextLedgerId = ledgers.ceilingKey(nextPosition.getLedgerId() + 1);
@@ -2775,7 +2775,7 @@ public class ManagedLedgerImpl implements ManagedLedger, CreateCallback {
         return nextPosition;
     }
 
-    PositionImpl getFirstPosition() {
+    public PositionImpl getFirstPosition() {
         Long ledgerId = ledgers.firstKey();
         if (ledgerId == null) {
             return null;