Add logging for splitscreen

- Log split enter/resize/swap/change/exit as per
  go/dragdrop_splitscreen_logging
- Pass drag session id and drop info to splitscreen controller

Bug: 191686897
Test: statsd_testdrive -e -terse 388 (and verify events from manual
      interaction)
Test: atest WMShellUnitTests
Change-Id: I2d11bffa2fa41a2cd77e78b12d94082d19dc2d6c