[autofit] Add embedded array of segments and edges.

Avoids multiple mallocs per typical glyphs.

With this and recent changes to avoid mallocs, the thread-safe
stack-based loader is now as fast as the previous model that had one
cached singleton.

* src/autofit/afhints.h (AF_SEGMENTS_EMBEDDED, AF_EDGES_EMBEDDED):
New macros.
(AF_AxisHintsRec): Add two arrays for segments and edges.

* src/autofit/afhints.c (af_axis_hints_new_segment): Only allocate
data if number of segments exceeds given threshold value.
(af_axis_hints_new_edge):  Only allocate data if number of edges
exceeds given threshold value.
(af_glyph_hints_done): Updated.
3 files changed