Replace "UTF8" with StandardCharsets.UTF_8

Avoids NON-NLS and possible UnsupportedEncodingException

bundles/org.eclipse.osgi/supplement/src/org/eclipse/osgi/util/ManifestElement.java

@@ -18,6 +18,7 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Enumeration;
@@ -605,7 +606,7 @@ private static String readLine(InputStream input, ByteArrayOutputStream buffer)
  }
  buffer.write(c);
  }
- String result = buffer.toString("UTF8"); //$NON-NLS-1$
+ String result = buffer.toString(StandardCharsets.UTF_8);
  buffer.reset();
  return result;
  }