[sanitizer] Add a fast version of StackDepotGet() for use in LSan.

Add a class that holds a snapshot of the StackDepot optimized for querying by
ID. This allows us to speed up LSan dramatically.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@189217 91177308-0d34-0410-b5e6-96231b3b80d8