Merge #16400: refactor: Rewrite AcceptToMemoryPoolWorker() using smaller parts

4a87c5c [refactor] Rewrite AcceptToMemoryPoolWorker() using smaller parts (Suhas Daftuar)

Pull request description:

  This is in preparation for re-using these validation components for a new version of AcceptToMemoryPool() that can operate on multiple transactions ("package relay").

ACKs for top commit:
  MarcoFalke:
    re-ACK 4a87c5c (did the rebase myself and arrived at the same result, mod whitespace)
  laanwj:
    ACK 4a87c5c

Tree-SHA512: b0495c026ffe06146258bace3d5e0c9aaf23fa65f89f258abc4af5980812e68e63a799f1d923e78ac1ee6bcafaf1222b2c2690a527df9b65dff7b48a013f154e

Author: laanwj