[svg] Set linear advances when loading SVG glyphs

* include/freetype/freetype.h (FT_GlyphSlotRec_): update doc
* src/cff/cffgload.c (cff_slot_load): do it
* src/truetype/ttgload.c (TT_Load_Glyph): do it

Fixes: #1156
3 files changed