Fix documentation on RegularPolygon (#8164)

A `RegularPolygon` is described by the circumscribed radius, not the
inscribed radius.

## Objective

- Correct documentation for `RegularPolygon`

## Solution

- Use the correct term

---------

Co-authored-by: Paul Hüber <phueber@kernsp.in>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

crates/bevy_render/src/mesh/shape/regular_polygon.rs

@@ -4,7 +4,9 @@ use wgpu::PrimitiveTopology;
 /// A regular polygon in the `XY` plane
 #[derive(Debug, Copy, Clone)]
 pub struct RegularPolygon {
-    /// Inscribed radius in the `XY` plane.
+    /// Circumscribed radius in the `XY` plane.
+    ///
+    /// In other words, the vertices of this polygon will all touch a circle of this radius.
     pub radius: f32,
     /// Number of sides.
     pub sides: usize,