Extract HardwareState conversion into a class and test it

Putting the conversion logic into its own class makes it more obvious
which variables are used for HardwareState conversion, and also provides
a clean public API to write tests against.

Bug: 251196347
Test: m inputflinger_tests && \
    $ANDROID_HOST_OUT/nativetest64/inputflinger_tests/inputflinger_tests \
    --gtest_filter='*HardwareStateConverterTest*'
Test: atest inputflinger_tests
Change-Id: I26771887b6b2eae46c9cec7190499da0016fdb1f