Add ASAN support to the zend allocator

[danog]

This pull request adds ASAN support to the zend allocator, by automatically poisoning all unused pages, chunks and heap management structures before exiting the alloc, free, etc (all ZEND_API) functions.

Internally, the implementation uses the following rules:

• Always poison memory (re)allocated by private (non-ZEND_API) allocation functions before returning it
• Unpoison memory (re)allocated by public (ZEND_API) allocation functions before returning within the ZEND_API function
• Always poison freed memory
• Always poison unused memory during reallocation (where new_size < old_size)
• When accessing private heap structures and fields, always unpoison before accessing and repoison immediately after
  • An exception to the above (for simplicity) is the main heap datastructure, which is poisoned only when entering a ZEND_API function and repoisoned before exiting

This is what allowed me to find #18833, before I found the fast shutdown workaround.

[danog]

@dstogov / @nielsdos / @iluuu1994 This is now ready for review!

The implementation is finalized, and has actually revealed a shutdown memory leak in php-fpm when terminated via a SIGTERM, due to the fact that alloc_globals_dtor is not getting invoked (the leak is surprisingly revealed exclusively by the usage of the poison functions, in fact, altering the ZEND_MM_POISON/ZEND_MM_UNPOISON macros to be no-ops re-hides the issue again, i.e. it's not caused by the other code changes/reorganization).

This PR also includes the changes from #18834, as the bug is detectable by ASAN now.

Side note, tracked_malloc also poisons/unpoisons the heap to avoid issues with the observe proxies.

[arnaud-lb]

Nice! This adds a bit of complexity but this seems worth it. I would suggest we run this in nightly. We could add a step to the existing ASAN jobs that runs the test suite without --asan (which sets USE_ZEND_ALLOC=0).

This looks good to me apart from a few comments.