net_processing: Move some static functions to PeerManager

Summary:

• BlockRequestAllowed
• AlreadyHaveBlock
• AlreadyHaveProof
• PrepareBlockFilterRequest
• ProcessGetBlockData
• ProcessGetCFilters
• ProcessGetCFHeaders
• ProcessGetCFCheckPt

Moved out of anonymous namespace:

• ProcessBlockAvailability
• UpdateBlockAvailability
• CanDirectFetch

This is a backport of core#21270 [10/12]
https://github.com/bitcoin/bitcoin/pull/21270/commits/021a04a46915468e7508a6ef44e7fbab1426343d

Depends on D11493

Test Plan:
With clangh and debug (for thread safety analysis)
ninja all check-all

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D11495