Add new load flag `FT_LOAD_NO_SVG`.

Modern color fonts often contain both an 'SVG' and 'COLR' table.  FreeType
always preferred 'SVG' over 'COLR' (this was a design decision), however,
this might not be the right choice for the user.  The new flags makes
FreeType ignore the 'SVG' table while loading a glyph.

Fixes #1229.

* include/freetype/freetype.h (FT_LOAD_NO_SVG): New macro.

* src/base/ftobjs.c (FT_Load_Glyph), src/cff/cffgload.c (cff_slot_load),
src/truetype/ttgload.c (TT_Load_Glyph): Use it.