Auto merge of #24217 - tdelacour:ISSUE-23995, r=jdm

ISSUE-23995: lazily generate UniqueIds for Nodes

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Updated `Node` so that its `unique_id` is only generated when `unique_id()` is called. This getter now also has assumed the responsibility for saving the `id` to the global hashset on `ScriptThread`.

Felt like I was fighting the borrow-checker a little bit on this one. Definitely a good learning experience for me, but the result strikes me as a little messy?

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- [X] These changes fix #23995 (GitHub issue number if applicable)

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