Make some fields more generic, so that we can access them the same
way regardless of Type 1 or CFF.
* include/freetype/internal/psaux.h (PS_Builder): Change `TT_Face'
to `FT_Face'.
Remove unused fields.
* src/psaux/psft.c: Update all accesses of `PS_Builder.face'.
Add some asserts to guard against casting `T1_Face' as `TT_Face'.
* src/type1/t1objs.h (T1_GlyphSlot): Reorder fields to follow
`CFF_GlyphSlot', so that we can pretend they are the same in the
interpreter.
* src/psaux/psobjs.c (ps_builder_init, ps_builder_add_point):
Updated with above changes.
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