move-only: unittest: add test/util/chainstate.h

and move CreateAndActivateUTXOSnapshot() into it for reuse
in future test modules.

test: refactor: declare NoMalleation const auto

To avoid linker error on some platforms:

https://github.com/bitcoin/bitcoin/pull/21526#discussion_r709404714

Co-authored-by: Russ Yanofsky <russ@yanofsky.org>

This is a backport of core#21526 [9 & 10/12]
https://github.com/bitcoin/bitcoin/pull/21526/commits/071200993f3a9412821ce5387851d659baf85327
https://github.com/bitcoin/bitcoin/pull/21526/commits/298bf5d563cc740c6ae71750d86942e0278b22d6

Backported out of order (refactoring commits first)

ninja check