* src/base/ftmm.c: Include FT_SERVICE_METRICS_VARIATIONS_H.
(ft_face_get_mvar_service): New auxiliary function to look up
metrics variation service.
(FT_Set_Var_Design_Coordinates, FT_Set_MM_Blend_Coordinates,
FT_Set_Var_Blend_Coordinates): Call metrics variation service.
* src/truetype/ttobjs.c (tt_face_init): Use metrics variations for
named instances.