[autofit] Code shuffling to reduce use of cpp macros. * src/autofit/afglobal.c (af_face_globals_compute_style_coverage): Call `af_get_coverage' unconditionally. * src/autofit/autofit.c: Include `hbshim.c' unconditionally. * src/autofit/hbshim.c (af_get_coverage) [!FT_CONFIG_OPTION_USE_HARFBUZZ]: Provide dummy function. * src/autofit/hbshim.h: Provide function declarations unconditionally.