Imported wallets used to send change back to the "from address".
We keep this behaviour as default.
There has already been an option "Use change addresses" (exposed in GUI),
ignored so far by imported wallets (was only used by HD wallets).
With this change, imported wallets no longer ignore that option, and if set,
they will send change to a random unused imported address, instead of back to "from address".
If all addresses are used, it falls back to sending change back to the "from address".
see: https://github.com/spesmilo/electrum/pull/7330
see: https://github.com/spesmilo/electrum/issues/5353
fbd8c5f7b0