Move MotionEvent#split implementation to native

There is already a native implementation of split in InputDispatcher.
Prevent code duplication by moving the Java impl to native. The Java
impl is not correct, because it cannot access all values like the
transforms to initialize the split event with.

Bug: 326171104
Test: atest libinput_tests
Test: atest inputflinger_tests
Change-Id: I6230b6aa0696dcfc275a5a14ab4af3d4b7bd0b45