gdiplus: add a drawing test for GdipFillRectangleI

[Nikolay Sivov]

Vincent Povirk wrote:
> This is a very simple drawing test that I've created to establish a precedent for drawing tests in gdiplus.
>
> Gdiplus currently has no tests that draw things and then check what was drawn. I've added some functions that should make this easy. It's important to get this right the first time so any feedback will be most appreciated.
>   
As for me I'm not against it if it'll work stably, but will this really 
help? It's much easier to check this visually, comparing with native output.
These pixel-by-pixel tests should use current bpp depth for 'relaxation' 
when we start draw gradients for example...That's will add another 
complexity.
Maybe it makes sense to add an antialiasing drawing tests to find out a 
closer algorithm for line drawing with different SmoothingModes...