[Profiler] Add export_memory_timeline to save memory timeline plot to file (#96137)
Summary: Added the functionality to export the memory timeline plot as a list of times and sizes, which the post processing visualization can parse and plot.
Test Plan: CI Tests
Reviewed By: leitian, fengxizhou
Differential Revision: D43680760
Pulled By: aaronenyeshi
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96137
Approved by: https://github.com/chaekit
