PointerChoreographerTest: Use builders to generate motion and key args

NotifyMotionArgs in particular have specific requirements, like needing
at least one pointer. Use a builder to generate these, instead of
relying on the default-constructed object.

Bug: 309479677
Test: atest inputflinger_tests
Change-Id: I5eccaff0eff2d87aa8d6c13a9659eed34e45c3da