feat(cdk/tree): implement the various skeleton methods

[BobobUnicorn]

[andrewseguin]

@BobobUnicorn Are these draft PRs still being worked on? Feel free to sync with me via Chat if you want guidance going forward on this tree redesign

[BobobUnicorn]

Yeah, I'd been out for a little while; I'll get these cleaned up for review.

[andrewseguin]

CI seems to be failing - want to try rebasing and trying it again?

[BobobUnicorn]

@andrewseguin I think the cdk-tree-revamp branch in this repo would also need to be rebased.

[andrewseguin]

@BobobUnicorn Did you need help rebasing the branch? Looks like this PR is in a distorted place with 2,000 files and 500 commits

[BobobUnicorn]

@andrewseguin I do not have permissions to update the branch in this repository

[andrewseguin]

Ah gotcha, would you like to open a PR from your local rebased branch that just updates this branch

[BobobUnicorn]

#25613 should do it

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