test: check anchors.dat when node starts for the first time
test: check anchors.dat when node starts for the first time

Summary:
Backport of [[https://github.com/bitcoin/bitcoin/pull/22118 | core#22118]].

Depends on D10959.

Ref T1696.

Test Plan:
  ./test/functional/test_runner.py feature_anchors

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Maniphest Tasks: T1696

Differential Revision: https://reviews.bitcoinabc.org/D10960

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