Store pointers in vector inside MotionEntry

For better support of arbitrary number of pointers, and for easier
interfacing with the rest of the system, convert MotionEntry to use
std::vector for PointerCoords and PointerProperties.

Bug: 211379801
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I91b4a88ec5df3f017ade8a6e55be3d3c1281de75