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.
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