wingdi: fix BGRA mask
It's the same as in bitmapheaderinfo and cleaner to read.
Ref #28367
v2
- no longer use a mask, always use BI_RGB and adjust the input format to match what Windows expects
- 16 bits only use 15 bits (!)
- drop 15 bit depth that will never happen
- request BGRX for 32-bits (it already works as swscale can do the conversion)
Edited by Steve Lhomme