Refactor ProcessNewBlock calls to reduce code duplication and take a CBlock reference

Summary:
core#21713

Refactor ProcessNewBlock to reduce code duplication

core#22106

validation: change ProcessNewBlock() to take a CBlock reference

Update ProcessNewBlock arguments to newer style.

net: cleanup newly added PeerManagerImpl::ProcessBlock

Addresses some post-merge comments.

This is a backport of core#21713 and core#22106

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12184