Image vectorscope is getting some visual updates (#116974), here
make the Sequencer vectorscope match the look fairly closely:
- Use same scaling factor for both U & V, instead of trying to use
all the texture space.
- Instead of drawing hexagonal area between color primary "pure"
and "75% saturation safe" points, draw a circle with colored
background and five inner rings.
- Indicate "75% saturation primaries" as wire rectangles with a
text label.
Aras Pranckevicius