Use a const InputDeviceContext ref in HardwareStateConverter

This involved changing a number of other references that could have been
const but weren't, hence this being a separate CL from the original.

Bug: 251196347
Test: build succeeds
Test: m inputflinger_tests && \
      $ANDROID_HOST_OUT/nativetest64/inputflinger_tests/inputflinger_tests \
      --gtest_filter='*HardwareStateConverterTest*'
Change-Id: Id4ecad74c9be19bd26aac525f0ebf44536677f85