Fix user-change handling for colliders as well as disabled colliders (#900)

* feat: add debug-demo for disabling a collider

* feat: add a simple debug-demo with two cubes

* feat: rename RigidBodyChangnes::MODIFIED and ColliderChanges::MODIFIED to ::IN_MODIFIED_SET

* feat: render debug-colliders with a different color with the debug-renderer

* chore: wire up new examples to the testbed

* fix colliders user-modification being ignored after the first step

* fix broad-phase still taking into account disabled colliders with enabled dynamic rigid-bodies

* chore: update changelog

* fix cargo doc

examples3d/debug_two_cubes3.rs

@@ -0,0 +1,29 @@
+use rapier_testbed3d::Testbed;
+use rapier3d::prelude::*;
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let impulse_joints = ImpulseJointSet::new();
+    let multibody_joints = MultibodyJointSet::new();
+
+    // Dynamic box rigid body.
+    let rigid_body = RigidBodyBuilder::dynamic().translation(vector![0.0, 2.0, 0.0]);
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(0.5, 0.5, 0.5);
+    colliders.insert_with_parent(collider, handle, &mut bodies);
+
+    let rigid_body = RigidBodyBuilder::fixed();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(0.5, 0.5, 0.5);
+    colliders.insert_with_parent(collider, handle, &mut bodies);
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, impulse_joints, multibody_joints);
+    testbed.look_at(point![10.0, 10.0, 10.0], Point::origin());
+}