[autofit] Introduce neutral blue zones to the latin module. Such blue zones match either the top or the bottom of a contour. We need them for scripts where accent-like elements directly touch the base character (for example, some vowel signs in Devanagari, cf. U+0913 or U+0914). * src/autofit/afblue.hin (AF_BLUE_PROPERTY_LATIN_NEUTRAL): New property. * src/autofit/afblue.h: Regenerated. * src/autofit/aflatin.h (AF_LATIN_IS_NEUTRAL_BLUE): New macro. (AF_LATIN_BLUE_NEUTRAL): New enumeration value. * src/autofit/aflatin.c (af_latin_metrics_init_blues, af_latin_hints_compute_blue_edges): Handle neutral blue zones.