BitMap.GetPixel Documentation

Originally reported at https://developercommunity.visualstudio.com/t/BitMapGetPixel-Documentation/10662841.
Moving here as part of the triage.

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> [severity:It’s more difficult to complete my work]
> Please note the BitMap.GetPixel documentation does not indicate whether “Y” starts at the top or bottom of image. Generally, I assume it starts at the top but, uh, assuming is always a mistake, and something like Postscript would reverse this as “Y” Is bottom. Also, if looking at a geometric grid, positive “Y” is always above the origin, which would make me think again that “Y” should start at the bottom and go up - so which is it? I also assume “X” starts on the left side of the image, but again you force me to assume, and if I was of Arabic origin this would be backwards to normal thinking. In any event the documentation should make this clear and not force us to guess…