SF/CE: Fix startup race in HwcAsyncWorker

If a HwcAsyncWorker is created, and shortly after `HwcAsyncWorker::send`
is called to queue up a task to run, there is a chance that the thread
that is created to run the tasks hasn't gotten to waiting on the
internal condition variable before the `notify_one` call is made to wake
up any waiting threads.

The result is that the HwcAsyncWorker thread doesn't get notified, and
goes to sleep. Meanwhile the SurfaceFlinger main thread waits forever
for the task to complete. Eventually the System Services start timing
out as SurfaceFlinger isn't processing requests.

The fix is simple -- switch to the two argument (predicate) form of
`std::condition_variable::wait()`, with the predicate checking for a
task (and the done flag). The predicate is checked before actually
waiting on the condition variable.

Additionally a unit test is added to verify this and a few other edge
conditions. The test fails (times out) without the implementation fix
when run with `atest`, and passes/completes with it.

Note that this is normally an uncommon error particularly on most
devices as HwcAsyncWorkers are only created when new outputs (virtual or
physical displays) are created, and there is usually a big gap between
when the HwcAsyncWorker is created and when it is actually used. It
ended up being more of a problem on Chromebooks as we create outputs for
every new app window, which happens much more frequently, and with a
much shorter delay between creation and use.

Flag: EXEMPT bugfix
Bug: 333824019
Test: atest libcompositionengine_test
Test: Smoke test of running DOTA Underlords on a Trogdor Chromebook
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:e0b2747abd28f4595a6f18f3f9fbe8aa15ae7000)
Merged-In: If3ad46a1297a0448dbdb505957081329f4cd2aca
Change-Id: If3ad46a1297a0448dbdb505957081329f4cd2aca