[PA] Scoped Scheduler-Loop Quarantine opt-out

This CL adds a new utility called `base::ScopedSafetyChecksExclusion`,
which allows function-granuality opt-out for safety checks (i.e.
scheduler-loop quarantine).

Internally, the scoped struct increments a counter in ctor and
decrement it in dtor. When the counter is non-zero, the quarantine
becomes no-op (immediate free).

Bug: 351974425
Change-Id: Ifae883a68076e80f44ba7e55b0c3400be86cde7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6467777
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Mikihito Matsuura <mikt@google.com>
Cr-Commit-Position: refs/heads/main@{#1452444}