Improve collision generation usability in the new 3D scene import workflow.

With this PR it's possible to add a collision during the Mesh import, directly in editor.
To generate the shape is possible to chose between the following options:
- Decompose Convex: The Mesh is decomposed in one or many Convex Shapes (Using the VHACD library).
- Simple Convex: Is generated a convex shape that enclose the entire mesh.
- Trimesh: Generate a trimesh shape using the Mesh faces.
- Box: Add a primitive box shape, where you can tweak the `size`, `position`, `rotation`.
- Sphere: Add a primitive sphere shape, where you can tweak the `radius`, `position`, `rotation`.
- Cylinder: Add a primitive cylinder shape, where you can tweak the `height`, `radius`, `position`, `rotation`.
- Capsule: Add a primitive capsule shape, where you can tweak the `height`, `radius`, `position`, `rotation`.

It's also possible to chose the generated body, so you can create:
- Rigid Body.
- Static Body.
- Area.

editor/plugins/mesh_instance_3d_editor_plugin.cpp

@@ -202,7 +202,8 @@ void MeshInstance3DEditor::_menu_option(int p_option) {
 				return;
 			}
 
-			Vector<Ref<Shape3D>> shapes = mesh->convex_decompose();
+			Mesh::ConvexDecompositionSettings settings;
+			Vector<Ref<Shape3D>> shapes = mesh->convex_decompose(settings);
 
 			if (!shapes.size()) {
 				err_dialog->set_text(TTR("Couldn't create any collision shapes."));