Never use String#getBytes() in the production code (facebook#9487)

Summary:
There are encodings that are not ASCII-compatible (like cp1140), so it is possible that a JVM is run with a default encoding in which String#getBytes() would return unexpected values even for ASCII strings.

A little bit of context: https://stackoverflow.com/questions/70913929/can-an-encoding-incompatible-with-ascii-encoding-be-set-as-a-default-encoding-in/70914154

Pull Request resolved: facebook#9487

Reviewed By: riversand963

Differential Revision: D34097728

fbshipit-source-id: afd654ecaf20f6d30d9fc20c6a090398de2585eb

java/src/main/java/org/rocksdb/RocksDB.java

@@ -14,14 +14,16 @@
 import java.util.concurrent.atomic.AtomicReference;
 import org.rocksdb.util.Environment;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
 /**
  * A RocksDB is a persistent ordered map from keys to values.  It is safe for
  * concurrent access from multiple threads without any external synchronization.
  * All methods of this class could potentially throw RocksDBException, which
  * indicates sth wrong at the RocksDB library side and the call failed.
  */
 public class RocksDB extends RocksObject {
-  public static final byte[] DEFAULT_COLUMN_FAMILY = "default".getBytes();
+  public static final byte[] DEFAULT_COLUMN_FAMILY = "default".getBytes(UTF_8);
   public static final int NOT_FOUND = -1;
 
   private enum LibraryState {