Add direct test coverage for non-merging/unsampling APIs of StackTraceTable.
Add direct test coverage for non-merging/unsampling APIs of StackTraceTable.

These are exercised by the profilers, but this coverage is indirect.

PiperOrigin-RevId: 341643478
Change-Id: I130fef8f34c9e637a88fd8e014bf40827b901d73

google/tcmalloc,google/tcmalloc,google/tcmalloc