Extract Gesture handling code and test it

Similarly to the HardwareState logic, extracting this code makes things
a bit clearer and easier to test.

Bug: 251196347
Test: m inputflinger_tests && \
    $ANDROID_HOST_OUT/nativetest64/inputflinger_tests/inputflinger_tests \
    --gtest_filter='*HardwareStateConverterTest*'
Test: atest inputflinger_tests
Change-Id: I6902e052fc5e193228aca4378587413b22889b26