Add an app that has two windows where you can draw. It showcases the new
feature of drawing into two windows with two different devices (touch
and stylus) at the same time.

Previously, this feature was not available on the platform.

Bug: 211379801
Test: APP=MultiDeviceInput; m $APP && adb install $ANDROID_PRODUCT_OUT/system/app/$APP/$APP.apk
Change-Id: I68875e3bba08a9e5ad5c917866f132e91b7c032e

Before this CL, the MotionPredictor API was inconvenient to use. The
MotionPredictor.predict returned a list of MotionEvents, with one
MotionEvent per-device.

The goal was to force applications to consider multi-device streams.
However, even if the apps use this API, there's no way they can
currently test this behaviour, since the multi-device feature is not yet
available.

For the multi-device streams feature, the current plan is to provide a
new View callback to get these raw streams. In those streams, the
per-device MotionEvents would continue to look the same. However, the
events may now be interleaved between different devices. For example, a
sequence like this would be possible: DOWN(deviceId=2) ->
DOWN(deviceId=3) -> MOVE(deviceId=2).

That means that the app will likely have to do per-device bookkeeping
anyways. So the app might as well just create a per-device
MotionPredictor object, as well.

Bug: 167946763
Test: (cd frameworks/native/services/inputflinger && atest)
Change-Id: I34b8dc02d4f995146cb3eed33888ae34abde29d6

This API will provide access to motion predictions.

Bug: 167946763
Test: atest InputTests
Change-Id: Ib8bc0debd9714e76520baae6ab8122762525716d

The class MotionPredictor will be used to call into native code to
execute prediction algorithm.

The feature can be enabled by setting the appropriate config on the
device.

To enable the feature:
adb shell setprop persist.input.enable_motion_prediction true

Bug: 210158587
Test: m MotionPrediction && adb install $ANDROID_PRODUCT_OUT/system/app/MotionPrediction/MotionPrediction.apk
Change-Id: Iaee80d99b18da2f788fa8eacf2e14a6b5c6a7088