[net] Move ConnectionType and eviction logic to their own files

Summary:
This is a move-only commit, best reviewed with

git show --color-moved=dimmed_zebra

This concludes backport of core#25500
https://github.com/bitcoin/bitcoin/pull/25500/commits/c741d748d4d9836940b99091cc7be09c65efcb79
https://github.com/bitcoin/bitcoin/pull/25500/commits/0101d2bc3c3bcf698d6cc2a237a680fc52395987
Depends on D18242

Test Plan:

cmake .. -GNinja -DBUILD_CHAINSTATE
ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18243