3fe836b78d504942e8850b607453886969f57e27 [moveonly] Extract RescanWallet to handle a simple rescan (Ben Woosley)
Pull request description:
Where the outcome does not depend on the result, apart from a simple success check.
Tree-SHA512: e0d29c6fc0c7f99a730289e5a80deb586b2848aead56b5198a71ef01f65374812468dfd57be0b8b076eb9be4090d5101d28d979a1d5c3d2f1caeca77b303e90e
Backport of Core PR12658
https://github.com/bitcoin/bitcoin/pull/13658/