`FakeAsync.getClock` clock should elapse by `flushTimers` too.

[feinstein]

The docs of FakeAsync.getClock says that the clock will elapse by calls to elapse and elapseBlocking, but this limits our ability to test timers.

FakeAsync has flushTimers that's supposed to elapse all timers, so I would expect that clock would elapse by the time that all the timers have been flushed as well.

Is this something that the docs are missing or the code behaviour should change?