[truetype] Implement `VVAR' table support.

* src/truetype/ttgxvar.h (GX_HVarTable): Renamed to...
(GX_HVVarTable): ...This.
(GX_Blend): Add fields for `VVAR' table handling.
Other minor updates.

* src/truetype/ttgxvar.c (ft_var_load_hvar): Renamed to...
(ft_var_load_hvvar): ...This.
Handle VVAR loading also (controlled by an additional parameter).
(tt_hadvance_adjust): Renamed to...
(tt_hvadvance_adjust): ...This.
Handle application of advance height also (controlled by an
additional parameter).
(tt_hadvance_adjust, tt_vadvance_adjust): Wrappers for
`tt_hvadvance_adjust'.

* src/truetype/ttdriver.c (tt_service_metrics_variations): Updated.
4 files changed