Add 'svg' module for OT-SVG rendering.

* CMakeLists.txt (BASE_SRCS): Add svg module file.
* (ft2_public_headers): Add `otsvg.h`.

* modules.cfg (RASTER_MODULES): Add `svg` module.

* builds/meson/ Add svg module.

* include/freetype/config/ftmodule.h: Add `ft_svg_renderer_class`.
* include/freetype/fterrdef.h: Add `Invalid_SVG_Document` and
`Missing_SVG_Hooks` error codes.
* include/freetype/internal/fttrace.h: Add tracing for `otsvg`.
* include/freetype/internal/svginterface.h: New file.  It adds an interface
to enable the presetting hook from the `base` module.
* include/freetype/otsvg.h (SVG_Lib_Init_Func, SVG_Lib_Free_Func,
SVG_Lib_Render_Func, SVG_Lib_Preset_Slot_Func): New hooks for SVG rendering.
(SVG_RendererHooks): New structure to access them.

* src/base/ftobjs.c: Include `svginterface.h`.
(ft_glyphslot_preset_bitmap): Add code for presetting the slot for SVG
(ft_add_renderer): Updated.

* src/svg/*: New files.
17 files changed