net_processing: move MaybeSetPeerAsAnnouncingHeadersAndIDs into PeerManagerImpl

Summary:
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

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11437