feat: impl Default for RigidBodyBuilder and ColliderBuilder

src/dynamics/rigid_body.rs

@@ -1134,7 +1134,8 @@ pub struct RigidBodyBuilder {
     pub linear_damping: Real,
     /// Damping factor for gradually slowing down the angular motion of the rigid-body, `0.0` by default.
     pub angular_damping: Real,
-    body_type: RigidBodyType,
+    /// The type of rigid-body being constructed.
+    pub body_type: RigidBodyType,
     mprops_flags: LockedAxes,
     /// The additional mass-properties of the rigid-body being built. See [`RigidBodyBuilder::additional_mass_properties`] for more information.
     additional_mass_properties: RigidBodyAdditionalMassProps,
@@ -1170,6 +1171,12 @@ pub struct RigidBodyBuilder {
     pub additional_solver_iterations: usize,
 }
 
+impl Default for RigidBodyBuilder {
+    fn default() -> Self {
+        Self::dynamic()
+    }
+}
+
 impl RigidBodyBuilder {
     /// Initialize a new builder for a rigid body which is either fixed, dynamic, or kinematic.
     pub fn new(body_type: RigidBodyType) -> Self {