Some comments from @sipa in #12702.

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Yes, I think `importmulti` is superior in every way, except:
* Slightly less convenient to use (it requires redundant information, as you have to explicitly state what you want to import, and then give the keys/... to enable that).
* ~Doesn't support P2SH-P2WPKH yet~. Added in #14454

The latter can be fixed by just adding support for that case. The former can be improved by adding 'default' cases (e.g. if you prove a WIF private key, it can permit omitting the address, ...).

#include <chain.h>
#include <key_io.h>
#include <rpc/server.h>
#include <validation.h>
#include <script/script.h>
#include <script/standard.h>
#include <sync.h>
#include <util.h>
#include <utiltime.h>
#include <wallet/wallet.h>
#include <merkleblock.h>
#include <core_io.h>
#include <wallet/rpcwallet.h>
#include <fstream>
#include <stdint.h>
#include <boost/algorithm/string.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <univalue.h>
int64_t static DecodeDumpTime(const std::string &str) {