validation: Pass in chainstate to ::NotifyHeaderTip

Summary:
[META] This commit should be followed up by removing the comments and assertions meant only to show that the change is correct.

This is a backport of core#20749 [11/17]
https://github.com/bitcoin/bitcoin/pull/20749/commits/2a696472a1423e877bfa83f016f66c7e45be7369

Depends on D11182

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11183