[3.x] Fix is_visible_in_tree regression for out of tree

[lawnjelly]

Fixes small regression from #107324:

The cached is_visible_in_tree flag wasn't updated when Spatials were hidden or shown out of tree.

While it didn't cause any obvious problems, it was a change to previous behaviour, so is undesirable. Keeping the flag up to date outside the tree is unlikely to cause any performance issues.

Notes

• Caught this when testing a blob shadows project which set some lights to hidden while out of tree.
• The regression testing code I left in for DEV_ENABLED builds did its job.

[Calinou]

Code looks good to me.

[lawnjelly]

Thanks!