[memory profiling] C++ tracing support (#95357)
Adds the ability to quickly generate stack traces for C++,
and combine Python, TorchScript, and C++ frames into a single trace.
This makes it possible for the memory tracer to record allocations inside
C++ code (e.g. convolution temporaries, backward operators).
The unwinder code is ~10x faster than execinfo.h's backward because it
cache fast unwinder routines for instruction pointers that have already been seen.
It is also only 1.2--2x slower than copying the entire stack (the approach perf takes),
while using 2 orders of magnitude less space per stack.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95357
Approved by: https://github.com/bertmaher
