[asan] add a test for array cookie if the operator new is defined inside the class (the cookie should not be poisoned in such case); update the related comment in asan_poisoning.cc

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@218620 91177308-0d34-0410-b5e6-96231b3b80d8