Add compile time checking for `::mempool.cs` runtime locking assertions.

This PR is a subset of #12665. The PR was broken up to make reviewing easier.

The intention is that literally all `EXCLUSIVE_LOCKS_REQUIRED`/`LOCKS_EXCLUDED`:s added in this PR should follow either directly or indirectly from `AssertLockHeld(…)`/`AssertLockNotHeld(…)`:s already existing in the repo.

Consider the case where function `A(…)` contains `AssertLockHeld(cs_foo)` (without
first locking `cs_foo` in `A`), and that `B(…)` calls `A(…)` (without first locking `cs_main`):
* It _directly_ follows that: `A(…)` should have an `EXCLUSIVE_LOCKS_REQUIRED(cs_foo)` annotation.
* It _indirectly_ follows that: `B(…)` should have an `EXCLUSIVE_LOCKS_REQUIRED(cs_foo)` annotation.