feat(draw): add initial SDL renderer

It caches SW rendered bitmaps in textures.
The cache is also updated to support data and source separately.
E.g. source is a path to an image, and if that image changes all
related cache entries needs to found and invalidated.

Limitations of SDL rederer:
- not all draw task types are supported
- image transformation is not supported
- some textures (e.g. button matrix texts) are not detected as cached
- images are not cached
- images are supported only from path

src/lv_init.c

@@ -164,6 +164,10 @@ void lv_init(void)
     lv_draw_pxp_init();
 #endif
 
+#if LV_USE_DRAW_SDL
+    lv_draw_sdl_init();
+#endif
+
     _lv_obj_style_init();
 
     /*Initialize the screen refresh system*/