kasan: stop leaking stack trace handles

Commit 773688a6 ("kasan: use stack_depot_put for Generic mode") added
support for stack trace eviction for Generic KASAN.

However, that commit didn't evict stack traces when the object is not put
into quarantine.  As a result, some stack traces are never evicted from
the stack depot.

In addition, with the "kasan: save mempool stack traces" series, the free
stack traces for mempool objects are also not properly evicted from the
stack depot.

Fix both issues by:

1. Evicting all stack traces when an object if freed if it was not put
   into quarantine;

2. Always evicting an existing free stack trace when a new one is saved.

Also do a few related clean-ups:

- Do not zero out free track when initializing/invalidating free meta:
  set a value in shadow memory instead;

- Rename KASAN_SLAB_FREETRACK to KASAN_SLAB_FREE_META;

- Drop the kasan_init_cache_meta function as it's not used by KASAN;

- Add comments for the kasan_alloc_meta and kasan_free_meta structs.

[akpm@linux-foundation.org: make release_free_meta() and release_alloc_meta() static]
Link: https://lkml.kernel.org/r/20231226225121.235865-1-andrey.konovalov@linux.dev
Fixes: 773688a6

 ("kasan: use stack_depot_put for Generic mode")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>