Lag spike when creating collision shape for mesh instance

[HiNice2MeetU]

Godot version:
v3.2.3

OS/device including version:

Renderer: GLES3 Renderer,
OS: Ubuntu 20.04.1 LTS
Graphics: NVIDIA Corporation TU106 [GeForce RTX 2060 Rev. A]
Processor: AMD® Ryzen 7 2700x eight-core processor × 16

Using steam version of godot

Issue description:
When using the auto-created mesh instance thingy (the "mesh" button you get in the 3d tool bar) and selecting single convex it creates a 1-2 min freeze, then the environment proceeds to be SUPER laggy, especially when the mesh instance is slected

Steps to reproduce:

1. Make an new scene with a rigid body as the scene root
2. get a mesh instance
3. Set radius to 0.05 and mid height to 0.1
4. hit the mesh button
5. Select single convex sibling

Minimal reproduction project:

minimal.zip

[pouleyKetchoupp]

Reproduced in 3.2.3 and 3.2.4 beta 5.

The physics polygon created from a capsule mesh has 1950 points (from all the vertices), and the editor gets stuck for a while when creating the debug collision mesh.

Callstack:

 	QuickHull::build(const Vector<Vector3> & p_points, Geometry::MeshData & r_mesh) Line 251	C++
 	ConvexPolygonShape::get_debug_mesh_lines() Line 43	C++
 	Shape::get_debug_mesh() Line 67	C++
 	CollisionShape::_update_debug_shape() Line 243	C++
 	CollisionShape::_notification(int p_what) Line 96	C++
 	CollisionShape::_notificationv(int p_notification, bool p_reversed) Line 39	C++
 	Object::notification(int p_notification, bool p_reversed) Line 931	C++
 	Node::_propagate_enter_tree() Line 224	C++