[1/4] windowscodecs: Introduce 24bppRGB PixelFormat

[Vincent Povirk]

The series looks good to me. Of course, we can already read 8-bit
tiffs just fine, but I guess your app makes use of the 8bpp RGB
format.

We could probably avoid a double conversion between rgb and bgr when
reading an 8-bit tiff as rgb, by implementing and using the
IWICBitmapSourceTransform interface, but MSDN seems to claim that the
native TIFF decoder doesn't do this.