## Goal
Currently, there's no way in KCL to get fields of a plane, e.g. the underlying X axis, Y axis or origin.
This would be useful for geometry calculations in KCL. It would help KCL users write transformations between planes for rotating geometry.
For example, this enables
```kcl
export fn crossProduct(@vectors) {
a = vectors[0]
b = vectors[1]
x = a[1] * b[2] - (a[2] * b[1])
y = a[2] * b[0] - (a[0] * b[2])
z = a[0] * b[1] - (a[1] * b[0])
return [x, y, z]
}
export fn normalOf(@plane) {
return crossProduct([plane.xAxis, plane.yAxis])
}
```
## Implementation
My goal was just to enable a simple getter for planes, like `myPlane.xAxis` and yAxis and origins. That's nearly what happened, except I discovered that there's two ways to represent a plane: either `KclValue::Plane` or `KclValue::Object` with the right fields.
No matter which format your plane is represented as, it should behave consistently when you get its properties. Those properties should be returned as `[number; 3]` because that is how KCL represents points.
Unfortunately we actually require planes-as-objects to be defined with axes like `myPlane = { xAxis = { x = 1, y = 0, z = 0 }, ...}`, but that's a mistake in my opinion. So if you do use that representation of a plane, it should still return a [number; 3]. This required some futzing around so that we let you access object fields .x and .y as [0] and [1], which is weird, but whatever, I think it's good.
This PR is tested via planestuff.kcl which has a Rust unit test.
Part of the hole efforts, see https://github.com/KittyCAD/modeling-app/discussions/7543
4f4c44e7c7