Move drag event to InputDispatcher (1/n)

This CL adds the ability to send a DRAG event through the
InputChannel, and adds the appropriate processing logic to
InputPublisher and InputConsumer.

Bug: 158242495
Test: atest libinput_tests InputPublisherAndConsumerTest
Change-Id: I7aead341a9851facf654024c476bd6d7eaae4590
7 files changed