Reimplement Brush Color Settings

[Haoming02]

• Right now, the 3 brush color options in Settings -> img2img are not used at all. So I add them back to the ForgeCanvas to make them function again.
• Also added a new option to toggle between the high-contrast brush and the color brush for the Inpaint mode, as some users may feel uncomfortable with the checked pattern ( How change the Inpaint to use color brush again?🤔 #1528 )

[DenOfEquity]

Nice one, works well.
I'd argue for including scribble_color_fixed=True, scribble_alpha_fixed=True, scribble_softness_fixed=True on the Inpaint canvas.

edit:
As it turns out, I can make those changes.
Thank for PR, Haoming02.

[Haoming02]

scribble_color_fixed=True, scribble_alpha_fixed=True, scribble_softness_fixed=True

imho it is better to let the user change those parameters. Disabling those kinda defeats the point of using ForgeCanvas ...

now you never worry about brush color being invisible when it is similar to image color ( #853 )

One of the advantages of ForgeCanvas is that you can draw a mask on a white/bright image, without losing where the mask is.