[ASan][libcxx] Annotating std::vector with all allocators

This revision is a part of a series of patches extending
AddressSanitizer C++ container overflow detection
capabilities by adding annotations, similar to those existing
in std::vector, to std::string and std::deque collections.
These changes allow ASan to detect cases when the instrumented
program accesses memory which is internally allocated by
the collection but is still not in-use (accesses before or
after the stored elements for std::deque, or between the size and
capacity bounds for std::string).

The motivation for the research and those changes was a bug,
found by Trail of Bits, in a real code where an out-of-bounds read
could happen as two strings were compared via a std::equals function
that took iter1_begin, iter1_end, iter2_begin iterators
(with a custom comparison function).
When object iter1 was longer than iter2, read out-of-bounds on iter2
could happen. Container sanitization would detect it.

In revision D132522, support for non-aligned memory buffers (sharing
first/last granule with other objects) was added, therefore the
check for standard allocator is not necessary anymore.
This patch removes the check in std::vector annotation member
function (__annotate_contiguous_container) to support
different allocators.

Additionally, this revision fixes unpoisoning in std::vector.
It guarantees that __alloc_traits::deallocate may access returned memory.
Originally suggested in D144155 revision.

If you have any questions, please email:
 - advenam.tacet@trailofbits.com
 - disconnect3d@trailofbits.com

Reviewed By: #libc, #sanitizers, philnik, vitalybuka

Spies: hans, EricWF, philnik, #sanitizers, libcxx-commits

Differential Revision: https://reviews.llvm.org/D136765