[macosx] Enhance handling of UTF-8 characters in CDataTransfer.java

Suggestion to change the handling of UTF-8 characters in CDataTransfer.java

charset = new String((byte[]) transferable.getTransferData(javaTextEncodingFlavor), "UTF-8”);

should probably be changed to

   import java.nio.charset.StandardCharsets;
   [...]
   charset = new String((byte[]) transferable.getTransferData(javaTextEncodingFlavor), StandardCharsets.UTF_8);

to avoid the unnecessary charset lookup. Suggestion is made just to improve the codebase.