Add note to SphereMesh's radius pointing to the height property

**Your Godot version:**
4.5.1.stable

**Issue description:**
When using `SphereShape3D`, the `radius` property relates to the radius of the whole sphere.
When using `SphereMesh` however, the `radius` property relates to the radius of the sphere's equator. The `height` property handles, well the sphere's height.

As you may have guessed, when creating a sphere programmatically, my mesh was squished, since I'd handled my `SphereMesh` the way I'd handle a `SphereShape3D`

I wanted to add a small line to `SphereMesh.radius`'s description: "See also [member height]", or "[b]Note:[/b] to get a regular sphere, radius must be equal to half of [member height]".

Before making a PR with this change, I wanted first to run it by someone with more experience to know if it would be appreciated, or rather be deemed as unnecessary.

**URL to the documentation page (if already existing):**
[SphereMesh](https://docs.godotengine.org/en/stable/classes/class_spheremesh.html)
[SphereShape3D](https://docs.godotengine.org/en/stable/classes/class_sphereshape3d.html)