Revert "Revert "Make sure that const-class linkage is preserved.""

Fix jdwp getting multiple instances of the same class.
Fix counting "zygote"/"non-zygote" classes in class table.
Fix FindClass() to EnsureResolved() classes added by
a racing thread to the class table.

Test: m test-art-host
Test: art/tools/run-jdwp-tests.sh --mode=host --variant=X64 --debug
Bug: 30627598

This reverts commit ecffc670.

Change-Id: I15807949da4f163c2693fac2fbfc274f17685f8a