Add ChronicleHash.offHeapMemoryUsed() method; Centralized management of all direct memory and file resources of ChronicleMap in one Cleaner

src/main/java/net/openhft/chronicle/hash/ChronicleHash.java

@@ -52,6 +52,16 @@ public interface ChronicleHash<K, E extends HashEntry<K>, SC extends HashSegment
      */
     long longSize();
 
+    /**
+     * Returns the amount of off-heap memory (in bytes), allocated by this {@code ChronicleHash} or
+     * shared with with other ChronicleHashes, persisting to the same {@link #file()}.
+     *
+     * <p>After {@link #close()} this method returns 0.
+     *
+     * @return the amount of off-heap memory, used by this {@code ChronicleHash} (in bytes)
+     */
+    long offHeapMemoryUsed();
+
     /**
      * @return the class of {@code <K>}
      */