Do not slip touch into window with same input channel

When two windows have the same input channel, do not slip touch from one
of them into the other. We don't have a use case for that, and
supporting this behaviour would be harder than simply disabling it.

Without slipping, the input channel also receives a continuous gesture,
which is generally desirable. The original window may not know that
there's a clone out there with the same input channel, and therefore may
not know to remove FLAG_SLIPPERY whenever it desires to receive a
continuous gesture.

Bug: 274073185
Test: m inputflinger_tests && $ANDROID_HOST_OUT/nativetest64/inputflinger_tests/inputflinger_tests
Change-Id: I577724c1c2e77928e695c250b5f5fbe8f1592a2f