Editor: Add some gizmo handles for MeshInstance3D

[HolonProduction]

Adds gizmos handles for boxes, cylinders and capsules to MeshInstance3D:

Screencast.From.2025-04-18.14-52-45.mp4

Since cylinder meshes have a split radius for top and bottom this PR adds a new handle behavior to GizmoHelper3D called cone frustum. I was considering adding handles for top and bottom radius as well, but I didn't find a good way to handle overlap with the height handles when dragging them very small, so this behavior only features one handle to move the middle point as seen in the video.

[Calinou]

Tested locally, it works as expected (including undo/redo). This is a nice usability improvement 🙂

Code looks good to me.

Do you think you could add a gizmo for SphereMesh too? It's probably the most important one that's missing right now. The rest (PlaneMesh/QuadMesh, PrismMesh, TorusMesh, RibbonTrailMesh, TubeTrailMesh) can be left for a future PR.

[HolonProduction]

Do you think you could add a gizmo for SphereMesh too?

Might look into it in a future PR. Main reason for not having it in here, is that this PR started out as just adding glue code to Gizmo3DHelper so only primitives that are in there are added. The frustum addition just kinda happened, but I don't want to add another primitive for this PR.

Edit: Just noticed, it's kinda hilarious that we have shared gizmo logic and it still requires this much code to actually integrate.