Prevent accidentally click on window with split touch

Currently, inputflinger would send an ACTION_POINTER_UP event with
AKEY_EVENT_FLAG_CANCELED when we have at least 2 pointers down and
one becomes the accidental touch.

An input window could have FLAG_SPLIT that could split a multi touch
event into some single touch events, so we should check the cancel flag
in order to prevent it trigger an accidental click on the target window.

Bug: 161655782
Test: inputflinger_tests
Test: enable twoshay, test accidental touch on slipt window.
Change-Id: I95eae0c9aef1f888f352b31affcece893d557754