[grid] add GridRadial and GridPolar

[williaster]

🚀 Enhancements

• This PR adds <GridRadial /> and <GridPolar /> components to @vx/grid, and updates the RadialLine demo to be implemented using them.

🐛 Bug Fix

• Also fixes a bug in the @vx/shape/Arc component where passing any prop (e.g., innerRadius) as 0 has no effect because of the if/else logic. This is needed for the implementation of <GridRadial /> because in order to use d3's arc() function without data, you must fully specify inner/outerRadius and start/endAngle, so I included it in this PR.

Will push the doc changes later tonight.

[williaster]

to clarify what the grid on its own looks like

[hshoff]

Thought about this more, how about we rename <GridPolar/> to <GridAngle />?

Then we could make a <GridPolar /> which uses both <GridAngle /> and <GridRadial /> (like the cartesian coordinate counterpart <Grid /> which uses <GridRows /> and <GridColumns />).

[williaster]

I dig it, will update 👍

[williaster]

closed in favor of #1007