Properly initialize MotionClassifier

InputClassifier will now play a more active role in managing the
lifecycle of MotionClassifier.

In the previous version of the code, we had a circular reference:
MotionClassifier owned a wp<InputClassifier>, that sometimes got
promoted to sp<>.
But the InputClassifier was the official owner of MotionClassifier, and
owned a unique_ptr<MotionClassifier>.

The owner of InputClassifier in real code is InputManager, and in test
code, it's the test class. When the owner of InputClassifier destroyed
InputClassifier, this could sometimes happen at the time when the
MotionClassifier also held a reference to the InputClassifier. That
meant that the proper owner of InputClassifier was not invoking the
destructor.
Instead, the MotionClassifier was invoking the InputClassifier
destructor.

To fix the situation, we now do the following:

1. InputClassifier will never die before MotionClassifier.

2. MotionClassifier constructor is now allowed to block. It would block
for some time because calling getService takes a while. To account for
this, InputClassifier launches a new thread to create MotionClassifier.

3. When MotionClassifier is ready to process events, InputClassifier
updates mMotionClassifier, which makes it non-null.

4. We now create a separate death recipient, which is co-owned by
InputClassifier and MotionClassifier. This is done so that the refcount
of the deathrecipient does not affect the refcount of InputClassifier,
and thus enforces the ownership of InputClassifier by the InputManager.
Now, no one can call ~InputClassifier except for its real owner.

5. MotionClassifier will subscribe the death recipient to the death of the
HAL. InputClassifier will delete MotionClassifier if HAL dies.
MotionClassifier no longer holds on to the death recipient.

6. We move the loop of the MotionClassifier thread to focus only on
processing events. That thread will no longer do any initialization.

7. Remove the thread check inside MotionClassifier. It isn't really
useful, now that there's only 1 function for the entire thread.

Ownership summary: Both InputClassifier and MotionClassifier own
DeathRecipient. DeathRecipient has a reference to InputClassifier. Thus,
we must guarantee that DeathRecipient dies before InputClassifier.
InputClassifier owns MotionClassifier. This is OK, since even if
InputClassifier dies, it will first delete MotionClassifier. That will
cause MotionClassifier to release 1 refCount from DeathRecipient. That
means the only reference remaining to DeathRecipient will be inside
InputClassifier, so InputClassifier will always be alive until
DeathRecipient is dead. Similar argument applies if MotionClassifier and
DeathRecipient die in different order (as observed from
InputClassifier).

Tests:
1) Manually running inputflinger_tests on cuttlefish:
build/launch cuttlefish using go/acloud
m inputflinger_tests
adb push out/target/product/vsoc_x86/data/nativetest/inputflinger_tests/inputflinger_tests /data/nativetest/inputflinger_tests/inputflinger_tests
adb shell
/data/nativetest/inputflinger_tests # ./inputflinger_tests --gtest_filter=*InputClassifierTest* --gtest_repeat=1000 --gtest_break_on_failure
2) Boot flame and open logcat. Observe in logcat:
StartInputManagerService took to complete: 2ms
Previously, in synchronous approach ( b/130184032) it was
about 100 ms (so we did not regress).
3) Kill the HAL while system_server is running, and dumpsys input before
and after:
adb shell dumpsys input (observe that MotionClassifier is non-null on flame)
adb shell -t killall android.hardware.input.classifier@1.0-service
adb shell dumpsys input (observe that MotionCLassifier is null)

Bug: 148311342
Test: see "Tests" section above
Change-Id: Ic76b82bd5f2cd374e3b001400eb495ca36de7353
Merged-In: Ic76b82bd5f2cd374e3b001400eb495ca36de7353
(cherry picked from commit 1652397a)