Add outside targets explicitly

Before this CL, the action of adding outside targets was a by-product of
finding the touched window.

In this CL, the change is made to add these targets explicitly. This
simplifies some of the code and allows us to stop generating targets for
cases where isDown is false.

Eventually, we may consider adding the outside targets back into touch
state to unify the security checks.

Bug: 211379801
Test: atest inputflinger_tests
Change-Id: I1373c28d306e154dac8b35879bb7d0497d1ff832