Add multiple pointer support to LegacyResampler with tests

Added multiple pointer support to LegacyResampler and included the
corresponding unit tests to ensure correctness.

Bug: 297226446
Flag: EXEMPT refactor
Test: TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST --gtest_filter="ResamplerTest*"
Change-Id: Ib639942c31311dcdcf6d72ed33a4d4476b76fe7f
3 files changed