Merge #11022: Basic keypool topup

d34957e [wallet] [tests] Add keypool topup functional test (Jonas Schnelli)
095142d [wallet] keypool mark-used and topup (John Newbery)
c25d90f [wallet] Add HasUnusedKeys() helper (John Newbery)
f2123e3 [wallet] Cache keyid -> keypool id mappings (John Newbery)
83f1ec3 [wallet] Don't hold cs_LastBlockFile while calling setBestChain (John Newbery)
2376bfc [wallet] [moveonly] Move LoadKeyPool to cpp (Matt Corallo)
cab8557 [wallet] [moveonly] Move CAffectedKeysVisitor (Jonas Schnelli)

Pull request description:

  This PR contains the first part of #10882 :

  - if a key from the keypool is used, mark all keys up to that key as used, and then try to top up the keypool
  - top up the keypool on startup

  Notably, it does not stop the node or prevent the best block from advancing if the keypool drops below a threshold (which means that transactions may be missed and funds lost if restoring from an old HD wallet backup).

Tree-SHA512: ac681fefeaf7ec2aab2fa1da93d12273ea80bd05eb48d7b3b551ea6e5d975dd97ba7de52b7fba52993823280ac4079cc36cf78a27dac708107ebf8fb6326142b

test/functional/test_runner.py

@@ -79,6 +79,7 @@ BASE_SCRIPTS= [
     'rawtransactions.py',
     'reindex.py',
     # vv Tests less than 30s vv
+    'keypool-topup.py',
     'zmq_test.py',
     'mempool_resurrect_test.py',
     'txn_doublespend.py --mineblock',