Handle multiple memory IDs using pid (#2974)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2974

Handle multiple memory IDs by dumping them into different processes in trace view. This solution seemed the simplest, and since the time stamps match between processes it should be fairly straightforward to look through

An alternate solution I attempted was to place different memory spaces across each other separated by some horizontal "space". However, it quickly became ugly/difficult to differentiate which allocation was on which memory space - I think the above solution is probably the easier one to read.

Reviewed By: kimishpatel, Olivia-liu, hsharma35

Differential Revision: D55494986

fbshipit-source-id: 1847f8c13bfed4db3f3baa3a61bcff77da69ff68