Merge #13114: wallet/keystore: Add Clang thread safety annotations for variables guarded by cs_KeyStore

Summary:
968b76f77c Add missing cs_KeyStore lock (practicalswift)
4bcd5bb87d Add locking annotations for variables guarded by cs_KeyStore (practicalswift)

Pull request description:

• Add Clang thread safety annotations for variables guarded by cs_KeyStore
• Add missing cs_KeyStore lock

Tree-SHA512: 7d93513c2da0cd564b9f1e75aa5156a454a4133eb845020fde8872e685dd5758353e93c33364aeea4a812c08353a810494e503a5ce160cc5be0af5af4bb2e6d7

Backport of Core PR13114
https://github.com/bitcoin/bitcoin/pull/13114/

Test Plan:

../configure --enable-debug CXX=clang++ CC=clang
make clean
make check
test_runner.py

Run team city build-werror.

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4272