GPU: automatically draw images with GLSL shader depending on resolution

This adds a new "Automatic" image display method which uses GLSL shaders for
most images. It only does CPU side color management for higher res images
where sending big float buffers to the GPU is likely to be a bottleneck or
cause memory usage problem.

Automatic is the default now, previously it was 2D Texture.

source/blender/editors/include/BIF_glutil.h

@@ -167,6 +167,8 @@ void ED_draw_imbuf_ctx_clipping(const struct bContext *C,
                                 float zoom_x,
                                 float zoom_y);
 
+int ED_draw_imbuf_method(struct ImBuf *ibuf);
+
 /* OpenGL drawing utility functions. Do not use these in new code, these
  * are intended to be moved or removed in the future. */