Add tests for some split touch cases

Test the situations where the first touch is either going into an empty
area, or onto a non-touchable window.

Bug: 214087836
Test: atest inputflinger_tests
Change-Id: Ic734c0508af0d004c499a45067e006e6741e8457
(cherry picked from commit 59b8118f74adc02c882d24254eabef6f488a378a)