graphics/mypaint-brushes2: Add new port for mypaint-brushes v2

Add this new port as a dependency of graphics/mypaint.

mypaint-brushes V2 is mostly identical to 1.3 brushes with a few tweaks
for some new inputs available in mypaint 2.x, such as viewzoom and viewrotation
Existing mypaint-brushes V1 branch still maintained, and is required by
many GTK tools such as Gimp.

Major changes since v2.0.0

• Include Dieterle brushes
• reductions to the file sizes of the preview icons.

PR: 235805
Submitted by: Greg V <greg@unrelenting.technology>