fix(core): track the three child on platform parent before passing off to the ancestor

This establishes the relationship between the three child and the
platform parent so that destroying the platform parent will also remove
the child from the scene

Author: nartc

libs/core/src/lib/renderer/renderer.ts

@@ -276,6 +276,8 @@ export class NgtRenderer2 implements Renderer2 {
 		if (pRS[NgtRendererClassId.type] === 'platform' && cRS[NgtRendererClassId.type] === 'three') {
 			// if platform has parent, delegate to that parent
 			if (pRS[NgtRendererClassId.parent]) {
+				// but track the child for this parent as well
+				addRendererChildNode(parent, newChild);
 				return this.appendChild(pRS[NgtRendererClassId.parent], newChild);
 			}