test: improve mempool_updatefromblock efficiency by using getmempoolentry for specific txns

Summary:
This improvement shaves off almost one minute on my machine for one of the longest functional test.

Before:

$ testr.py mempool_updatefr*
Starting Bitcoin ABC functional tests

mempool_updatefromblock.py started
Running jobs: mempool_updatefromblock.py
mempool_updatefromblock.py passed, Duration: 277 s

After:

$ testr mempool_updatefr*
Starting Bitcoin ABC functional tests

mempool_updatefromblock.py started
Running jobs: mempool_updatefromblock.py
mempool_updatefromblock.py passed, Duration: 219 s

This is a single commit from core#22707. The other commits still have a year worth of unbackported dependencies, and have a lower impact.

https://github.com/bitcoin/bitcoin/pull/22707/commits/86dbd54ae8a8f9c693c0ea67114bbff24a0754df

Test Plan:

test/functional/test_runner.py  mempool_updatefromblock

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9935