Add Vector3.xy(Vector2) swizzle (#336)

src/main/java/org/joml/Vector3d.java

@@ -265,6 +265,33 @@ public double x() {
         return this.x;
     }
 
+    /**
+     * Copy the <code>(x, y)</code> components of <code>this</code> into the supplied <code>dest</code> vector
+     * and return it.
+     * <p>
+     * Note that due to the given vector <code>dest</code> storing the components in float-precision,
+     * there is the possibility to lose precision.
+     *
+     * @param dest
+     *      will hold the result
+     * @return dest
+     */
+    public Vector2f xy(Vector2f dest) {
+        return dest.set(x, y);
+    }
+
+    /**
+     * Copy the <code>(x, y)</code> components of <code>this</code> into the supplied <code>dest</code> vector
+     * and return it.
+     *
+     * @param dest
+     *      will hold the result
+     * @return dest
+     */
+    public Vector2d xy(Vector2d dest) {
+        return dest.set(x, y);
+    }
+
     public double y() {
         return this.y;
     }

src/main/java/org/joml/Vector3f.java

@@ -241,6 +241,30 @@ public float x() {
         return this.x;
     }
 
+    /**
+     * Copy the <code>(x, y)</code> components of <code>this</code> into the supplied <code>dest</code> vector
+     * and return it.
+     *
+     * @param dest
+     *      will hold the result
+     * @return dest
+     */
+    public Vector2f xy(Vector2f dest) {
+        return dest.set(x, y);
+    }
+
+    /**
+     * Copy the <code>(x, y)</code> components of <code>this</code> into the supplied <code>dest</code> vector
+     * and return it.
+     *
+     * @param dest
+     *      will hold the result
+     * @return dest
+     */
+    public Vector2d xy(Vector2d dest) {
+        return dest.set(x, y);
+    }
+
     public float y() {
         return this.y;
     }

src/main/java/org/joml/Vector3i.java

@@ -314,6 +314,42 @@ public int x() {
         return this.x;
     }
 
+    /**
+     * Copy the <code>(x, y)</code> components of <code>this</code> into the supplied <code>dest</code> vector
+     * and return it.
+     *
+     * @param dest
+     *      will hold the result
+     * @return dest
+     */
+    public Vector2f xy(Vector2f dest) {
+        return dest.set(x, y);
+    }
+
+    /**
+     * Copy the <code>(x, y)</code> components of <code>this</code> into the supplied <code>dest</code> vector
+     * and return it.
+     *
+     * @param dest
+     *      will hold the result
+     * @return dest
+     */
+    public Vector2d xy(Vector2d dest) {
+        return dest.set(x, y);
+    }
+
+    /**
+     * Copy the <code>(x, y)</code> components of <code>this</code> into the supplied <code>dest</code> vector
+     * and return it.
+     *
+     * @param dest
+     *      will hold the result
+     * @return dest
+     */
+    public Vector2i xy(Vector2i dest) {
+        return dest.set(x, y);
+    }
+
     public int y() {
         return this.y;
     }