[libc++] Remove UB in list, forward_list and __hash_table

This patch removes undefined behavior in list and forward_list and __hash_table
caused by improperly beginning and ending the lifetime of the various node
classes. It allows removing the _LIBCPP_STANDALONE_DEBUG macro from
these node types since we now properly begin and end their lifetime,
meaning that we won't trip up constructor homing.

See https://reviews.llvm.org/D98750 for more information on what prompted
this patch.

Differential Revision: https://reviews.llvm.org/D101206



Co-authored-by: Amy Kwan <amy.kwan1@ibm.com>