This commit completely separates the interaction between named
instances and variation functions. In particular, resetting the
variation returns to the current named instance (if set) and not to
the base font.
As a side effect, variation functions no longer change the named
instance index.
* src/cff/cffobjs.c (cff_face_init): Use MM service's `set_instance'
function.
Also apply `MVAR' table to named instances.
* src/truetype/ttgxvar.c (TT_Get_MM_Var): Add cast.
(tt_set_mm_blend): No longer check whether requested variation
coincides with a named instance.
(TT_Set_Var_Design): Use current named instance for default
coordinates.
* src/truetype/ttobjs.c (tt_face_init): Use `TT_Set_Named_Instance'.
f89c67f043