Design vector and quad glyph plot APIs

[meghanto]

I'm continuing on my quest to recover/rewrite all the past work I did, this time from mid-2022(!)

#1742 adds points/glyph_type to pseudocolor point-mesh plots for scalar, sphere, cube, and axes glyphs. Follow-up work would add oriented arrow glyphs for vector fields and expose Viskores quad glyphs. These would require ascent team to make design choices.

Vector glyphs

Vector arrows have a different field contract and controls from scalar pseudocolor plots: direction, magnitude scaling, normalization, and arrow dimensions.

We would most likely want a new plot type for vector glyphs instead of extending pseudocolor.

Quad glyphs

Viskores quads are camera-facing billboards with screen-space sizing behavior, unlike the world-space glyphs currently exposed by points/glyph_type.

Should quads be:

a) another point glyph_type with explicit size units/mode; or
b) a separate billboard/point-sprite plot type?

if a) , is it a good idea to overload the 'radius' field for both world-space dimensions as well as screen-space dimensions for quads? or (cleaner) disable radius for glyph_type:quad and create pixel_size and pixel_size_delta as parameters?

[meghanto]

@cyrush Bumping this to ask for thoughts on next step re: billboard glyphs.