MassProperties: modify the return types of 2 setters, to allow chaining

src/main/java/com/github/stephengold/joltjni/MassProperties.java

@@ -99,21 +99,27 @@ public void scaleToMass(float mass) {
      * Alter the inertia tensor. (native attribute: mIntertia)
      *
      * @param inertia the desired value (not null, unaffected, default=zero)
+     * @return the modified properties (for chaining)
      */
-    public void setInertia(Mat44Arg inertia) {
+    public MassProperties setInertia(Mat44Arg inertia) {
         long propertiesVa = va();
         long matrixVa = inertia.va();
         setInertia(propertiesVa, matrixVa);
+
+        return this;
     }
 
     /**
      * Alter the mass. (native attribute: mMass)
      *
      * @param mass the desired mass (in kilograms, ≥0, default=0)
+     * @return the modified properties (for chaining)
      */
-    public void setMass(float mass) {
+    public MassProperties setMass(float mass) {
         long propertiesVa = va();
         setMass(propertiesVa, mass);
+
+        return this;
     }
 
     /**