[Issue] black and white not handled well by "Adjust Curves"

[Cub0use]

• using one of the curves at all will make black pixels transparent

• white cannot be adjusted

https://user-images.githubusercontent.com/81629481/188213431-ae443d13-fb2f-41fe-9632-64bc4221b4c6.mp4

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Additionally, it would be good to be able to move the two keys at the extremities of a curve, like in photoshop:

This would make adjusting colors and opacity uniformly possible, and accurately handle black and white.

-Blockbench 4.4.0 beta 2, Desktop version, Windows 10