[8u] RFR(S) 8044107 : Add Diagnostic Command to list all ClassLoaders
Please review this very simple serviceability backport to 8u. The only
difference between the JDK 9 changeset and the JDK 8 changeset is that
the ClassLoaderDataGraph::cld_do function was already backported to JDK
8 in the fix for 8049421 . So the changes for adding
classLoaderData.hpp|cpp are already in JDK 8 line-for-line exactly the
same as they are in JDK 9.