Allows making lNodesAnnouncingHeaderAndIDs and nPeersWithValidatedDownloads member vars instead of globals.
Removes the need to pass conman as a parameter to the method.
This concludes a backport of core#20942 [8&9/9]
https://github.com/bitcoin/bitcoin/pull/20942/commits/39c2a69bc28eb3e3b5fa15a3965773b459bbf7ad
https://github.com/bitcoin/bitcoin/pull/20942/commits/6452190841f8da1cdaf899d064974136ab37659f
Depends on D11436