…159112)

* Update vendored mimalloc to v2.5.2

Upgrade mimalloc from v2.1.2 to v2.5.2 as-is from upstream.

v2.1.2: https://github.com/microsoft/mimalloc/releases/tag/v2.1.2
v2.5.2: https://github.com/microsoft/mimalloc/releases/tag/v2.5.2

* Re-apply CPython-specific changes to mimalloc v2.5.2

Most of the previous downstream changes were upstreamed in mimalloc
v2.1.3 - v2.1.7 (heap tags, _mi_heap_init/_mi_tld_init, MI_PRIM_THREAD_ID,
sub-processes, heap walk optimizations, platform fixes) and are dropped.

Remaining CPython-specific changes, all marked with a "CPython" comment:

- QSBR delayed page freeing for free-threaded builds (pythongh-115103,
  pythongh-145615): mi_page_t/mi_heap_t fields and _PyMem_mi_* hooks in
  page.c, heap.c and segment.c.
- debug_offset: preserve the first bytes of a PyObject (ob_tid, refcount
  fields) when filling freed or uninitialized memory in debug builds
  (pythongh-115491).
- Atomic mi_block_t.next loads/stores to avoid TSAN reports (pythongh-129748).
- Relax the owning thread assertion in _mi_free_delayed_block for
  free-threaded builds, since the GC traverses heaps of other threads.
- Call _mi_heap_delayed_free_partial() in mi_heap_visit_blocks()
  (pythongh-112532).
- Only count reclaimed pages up to MI_MEDIUM_OBJ_SIZE_MAX as a
  "right page" in mi_segment_reclaim (pythongh-115103).
- Rename the weak _ZSt15get_new_handlerv symbol and disable the
  mi_is_in_heap_region debug warning.
- Zero-initialize _mi_page_empty instead of a positional initializer.

* Update the free-threaded build to mimalloc v2.5.2 changes

mimalloc v2.1.4 replaced the list of abandoned segments with per-arena
bitmaps and introduced sub-processes (mi_subproc_t) to keep abandoned
segments of separate interpreters apart. Use them instead of the
CPython-specific mi_abandoned_pool_t:

- Each interpreter owns a mi_subproc_t created in init_interpreter().
- tstate_mimalloc_bind() sets tld->segments.subproc and uses the
  upstream _mi_heap_init() signature.
- The GC and sys.getallocatedblocks() visit abandoned segments with
  _PyMem_mi_visit_abandoned_blocks(), the upstream cursor API without
  the mi_option_visit_abandoned requirement, while STW.

* Update NEWS.d

* fix MSAN

* fix TSAN

* fix test_cext

* Disable THP

* Address code review

* Address code review

* Address code review

* nit

* Address code review

* Address code review
(cherry picked from commit aff7a2e)

Co-authored-by: Donghee Na <donghee.na@python.org>

…_ on Emscripten (from pythonGH-159039)