gdiplus: fix GdipFillRectangleI no effect on memory DC whose windoworigin point has changed

[Vincent Povirk]

-        rect->X = 0;
-        rect->Y = 0;
+        /*The user maybe has called SetWindowOrgEx to change origin point*/
+        POINT pt = {0, 0};
+        GetWindowOrgEx(graphics->hdc, &pt);
+        rect->X = pt.x;
+        rect->Y = pt.y;

I don't think we should use GetWindowOrgEx in gdiplus. There are too
many ways to change the mapping of co-ordinates for an HDC, and it
doesn't make sense to specifically account for them all.

In get_graphics_bounds, we already have code that accounts for the HDC
transform using DPtoLP. Maybe we should do that even when GetMapMode
== MM_TEXT.

Transforming the region in alpha_blend_pixels_hrgn looks wrong to me,
because we can't do that in the general case. Logical coordinates on
the HDC may not be pixels.

Your test is very unclear. A good test for this should make it obvious
how the HDC's transform affects GDI+ world coordinates. If I fill a
rectangle at (0,0) using GDI+, on an HDC with window origin (5,5),
what is the origin of that rectangle on the screen?