[net_processing] Move SendBlockTransactions into PeerManager

Summary:
Partial backport (8/9) of core PR19791:
https://github.com/bitcoin/bitcoin/pull/19791/commits/aa114b1c9b06c2bd3ed936bbb9fb32b31f75bdb2

Depends on D9047.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D9048