refactor: Move block storage globals to blockstorage

Summary:
However, keep a declaration in validation to make it possible to move
smaller chunks to blockstorage without breaking compilation.

Also, expose AbortNode in the header.

Can be reviewed with --color-moved=dimmed-zebra --color-moved-ws=ignore-all-space

This is a backport of core#21727 [2/4]
https://github.com/bitcoin/bitcoin/pull/21727/commits/fa247a327fc7c7cea6bc8f93637b8babd3015ffa

Depends on D12032

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D12033