[backport] wallet: upgradewallet fixes, improvements, test coverage #20490

1. 
   MarcoFalke commented at 11:51 am on November 25, 2020: member

   Github-Pull: #20403 Rebased-From: c46c18b788cb0862aafbb116fd37936cbed6a431

   Github-Pull: #20403 Rebased-From: 2498b04ce88696a3216fc38b7d393906b733e8b1

   Github-Pull: #20403 Rebased-From: 99d56e357159c7154f69f28cb5587c5ca20d6594

   Github-Pull: #20403 Rebased-From: ca8cd893bb56bf5d455154b0498b1f58f77d20ed

2. wallet: refactor GetClosestWalletFeature() c46c18b788
3. Don't upgrade to HD split if it is already supported

   It is unnecessary to upgrade to FEATURE_HD_SPLIT if this feature is
   already supported by the wallet. Because upgrading to FEATURE_HD_SPLIT
   actually requires upgrading to FEATURE_PRE_SPLIT_KEYPOOL, users would
   accidentally be upgraded to FEATURE_PRE_SPLIT_KEYPOOL instead of nothing
   being done.
   
   Fixes the issue described at
   https://github.com/bitcoin/bitcoin/pull/20403#discussion_r526063920

   2498b04ce8
4. wallet: fix and improve upgradewallet result responses 99d56e3571
5. wallet: fix and improve upgradewallet error responses ca8cd893bb
6. fanquake added the label Backport on Nov 25, 2020
7. MarcoFalke merged this on Nov 25, 2020
8. MarcoFalke closed this on Nov 25, 2020

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9. MarcoFalke deleted the branch on Nov 25, 2020
10. DrahtBot locked this on Feb 15, 2022

Contributors
MarcoFalke

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Backport