Rationalize lock anotation in validation code

Summary:
Make sure the annotation are set on declarations rather than implementations, and make sure there are lock assertions consistent with lock annotations.

Depends on D4592

Test Plan: Build with clang and ensure there are no warnings.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4581