simpleperf: Add trace-sched command.

trace-sched command traces system-wide process runtime events,
and reports potential spin loops.

Bug: http://b/74443296
Test: run simpleperf_unit_test.
Test: run `simpleperf trace-sched` manually.
Change-Id: I6d5205442fe17019f214e9966f93636b1db9f1ef
7 files changed