For functions querying a face, bits 16-30 of the face index can hold
the named instance index if we have a GX font. The indices start
with value 1; value 0 indicates font access without GX variation
data.
* include/freetype/freetype.h (FT_FaceRec): Update documentation.
* include/freetype/internal/sfnt.h: Ditto.
* src/sfnt/sfobjs.c (sfnt_init_face)
[TT_CONFIG_OPTION_GX_VAR_SUPPORT]: Get number of named instances and
do argument checks.
(sfnt_load_face): Updated.
* src/truetype/ttobjs.c (tt_face_init)
[TT_CONFIG_OPTION_GX_VAR_SUPPORT]: Use named instance, overwriting
the style name.
* src/base/ftobjs.c (open_face_from_buffer,
open_face_PS_from_sfnt_stream): Updated.
* src/bdf/bdfdrivr.c (BDF_Face_Init): Updated.
* src/cff/cffload.c (cff_font_load): Updated.
* src/cff/cffobjs.c (cff_face_init): Make function exit early for
pure CFF fonts if `font_index < 0'.
Updated.
* src/cid/cidobjs.c (cid_face_init): Updated.
* src/pcf/pcfdrivr.c (PCF_Face_Init): Updated.
* src/pfr/pfrobjs.c (pfr_face_init): Updated.
* src/type1/t1objs.c (T1_Face_Init): Updated.
* src/type42/t42objs.c (T42_Face_Init): Updated.
* src/winfonts/winfnt.c (fnt_face_get_dll_font, FNT_Face_Init):
Updated.
* docs/CHANGES: Updated.
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