[bevy_ui/layout] Handle ui heirchy change edge cases

[StrikeForceZero]

• I need to open an issue that documents the problem this is solving

Blocked on:

• [bevy_ui/layout] Add tests, missing asserts, missing debug field, and widen children param in update_children for UiSurface #12803
• [bevy_ui/layout] UiSurface update internal mappings #12804

---

Objective

• Handle UI Nodes being moved to a new parent Changed<Parent>
• Handle UI Nodes who lost their parent RemovedComponent<Parent>

Solution

• Adds query to the layout_system to handle the specified edge cases

Testing

• Did you test these changes? If so, how?
  • Added Tests
• Are there any parts that need more testing?
  • Identifying any potential regressions or unknown side effects
• How can other people (reviewers) test your changes? Is there anything specific they need to know?
  • Testing an example project that emulates a drag-and-drop-like behavior for UI node relationships.
  • Think of alternative edge cases that fit with the scope of this PR.
• If relevant, what platforms did you test these changes on, and are there any important ones you can't test?
  • Tested on Linux

---

Changelog

• Added handling of UI nodes changing parents
• Added handling of UI nodes removing parents

[StrikeForceZero]

I was planning on moving this logic into an associated function on UiSurface, especially with #13359, but passing the queries seems out of scope. I am open to suggestions.