[2/2] gdiplus: Add 8bpp to the list of supported formats.

[Vincent Povirk]

>> > +    &GUID_WICPixelFormat8bppGray,
>>
>> This will give you a halftone palette instead of a grayscale palette,
>> unless you add special handling for that format.
>
> That's fine for the time being.

Currently, the images should render correctly because WIC converts
them to 32-bit RGBA, so rendering of TIFF images in this format will
regress.