Support injecting jank into Scheduler for testing purposes

Injects a fraction of a frame's expected present time as a jank. This is
mainly to avoid thinking about hard-coding milliseconds.

Also supports delaying this jank injection, since the Perfetto UI
currently steals any ADB session

Bug: 296636083
Test: TouchLatency + perfetto
Change-Id: If08616e68c3e7b3d6eaed6f6ff5cbc6ad444481e