fa5e373365 validation: Add cs_main locking annotations (MarcoFalke)
fa5c346c5a doc: Add comment to cs_main and mempool::cs (MarcoFalke)
fafe941bdd test: Add missing validation locks (MarcoFalke)
fac4558462 sync: Add RecursiveMutex type alias (MarcoFalke)
Pull request description:
Both the chain state and the transaction pool are validation specific, but access to them is protected by two locks. The two locks have the following semantics:
* Writing to the chain state or adding transactions to the transaction pool -> Take both `cs_main` and `mempool::cs`
* Reading either or removing transactions from the the transaction pool -> Take only the appropriate lock
Tree-SHA512: 6f6e612ffc391904c6434a79a4f3f8de1b928bf0a3e3434b73561037b395e2b40a70a5a4bd8472dd230e9eacc8e5d5374c904a3c509910cf3971dd7ff59a626c