Pass mempool reference to chainstate constructor

Summary:

Next step toward core#19556

Instead of relying on the mempool global, each chainstate is given a reference to a mempool to keep up to date with the tip (block connections, disconnections, reorgs, ...)

This is a backport of core#19826

Most differences from Core in validation.cpp are explained by D1667, D7203 & D7439.

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9780