RFR (S) 8212988: add recent class unloading events to the hs_err log

[coleen.phillimore at oracle.com]

Summary: also moved class unloading logging in expected place.

Tested with assert to verify hs_err_file, some dacapo performance 
testing, and hs tier1-6.  See bug for details.

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8212988.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8212988

Thanks,
Coleen