[orx-shapes] Add extensions for creating sub-shapes and positioning boxes

Introduce `Rectangle.sub` and `Box.sub` functions to derive sub-rectangles and sub-boxes from existing shapes using relative dimensions. Add `Box.place` to position a box relative to another using customizable anchors.

orx-shapes/src/commonMain/kotlin/primitives/BoxPlace.kt

@@ -0,0 +1,13 @@
+package org.openrndr.extra.shapes.primitives
+
+import org.openrndr.math.Vector3
+import org.openrndr.shape.Box
+
+fun Box.place(item: Box, anchor: Vector3 = Vector3(0.5, 0.5, 0.5), itemAnchor: Vector3 = anchor): Box {
+    return Box(
+        corner = corner + (dimensions * anchor - item.dimensions * itemAnchor),
+        width = item.width,
+        height = item.height,
+        depth = item.depth
+    )
+}

orx-shapes/src/commonMain/kotlin/primitives/BoxSub.kt

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+package org.openrndr.extra.shapes.primitives
+
+import org.openrndr.shape.Box
+
+/**
+ * Creates a sub-box from the current box using the dimensions
+ * defined by another box.
+ *
+ * @param uvw The box defining the dimensions (relative to this box)
+ * to create the sub-box. Its position and size are used to compute the
+ * resulting sub-box.
+ */
+fun Box.sub(uvw: Box) =
+    sub(
+        uvw.corner.x,
+        uvw.corner.y,
+        uvw.corner.z,
+        uvw.corner.x + uvw.width,
+        uvw.corner.y + uvw.height,
+        uvw.corner.z + uvw.depth
+    )

orx-shapes/src/commonMain/kotlin/primitives/RectangleSub.kt

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+package org.openrndr.extra.shapes.primitives
+
+import org.openrndr.shape.Rectangle
+
+/**
+ * Creates a sub-rectangle from the current rectangle using the dimensions
+ * defined by another rectangle.
+ *
+ * @param uv The rectangle defining the dimensions (relative to this rectangle)
+ * to create the sub-rectangle. Its position and size are used to compute the
+ * resulting sub-rectangle.
+ */
+fun Rectangle.sub(uv: Rectangle) = sub(uv.x, uv.y, uv.x + uv.width, uv.y + uv.height)