NodeUtils: Ignore private sub properties in getNodeChildren().

[Mugen87]

Fixes #31522

Description

getNodeChildren() ignores private properties on object level but not on the level below. For consistency reasons, private sub properties should also be ignored.

Note: The PR does not fix #31522. However, consistently ignoring private properties makes it possible to workaround the issue, see #31522 (comment).

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.39 78.91	338.39 78.91	+0 B +0 B
WebGPU	566.1 156.49	566.16 156.5	+63 B +10 B
WebGPU Nodes	564.7 156.25	564.77 156.26	+63 B +11 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	469.82 113.62	469.82 113.62	+0 B +0 B
WebGPU	637.32 172.46	637.38 172.47	+63 B +12 B
WebGPU Nodes	591.96 161.7	592.02 161.71	+63 B +12 B

[sunag]

I added a conditional to check just pure objects.