RFR (XS) 8236968: jmap -clstats fails to work after JDK-8232759

[coleen.phillimore at oracle.com]

Summary: Make jmap -clstats call jcmd VM.classloader_stats instead which 
better matches the documentation

Tested with tier1 and * 
jtreg:open/test/jdk/sun/tools/jmap/BasicJMapTest.java
  locally.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8236968.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8236968

Thanks,
Coleen