[lsan] Reduce StopTheWorld access to StackDepot

StackDepot locks some stuff. As is there is small probability to
deadlock if we stop thread which locked the Depot.

We need either Lock/Unlock StackDepot for StopTheWorld, or don't
interact with StackDepot from there.

This patch does not run LeakReport under StopTheWorld. LeakReport
contains most of StackDepot access.

As a bonus this patch will help to resolve kMaxLeaksConsidered FIXME.

Depends on D114498.

Reviewed By: morehouse, kstoimenov

Differential Revision: https://reviews.llvm.org/D115284