Splits signrwatransaction into a wallet version (signrawtransactionwithwallet) and
non-wallet version (signrawtransactionwithkey). signrawtransaction will call the right signrawtransaction* command as per the parameters in order to
Updated signrawtransactions test to use new RPCs
Backport 1/3 of core PR10579 (partial backport of commit 1e79c05)
Note: in order to not break the tests, the signrawtransaction deprecation will be backported in a later diff, once all the tests are updated to the new RPC.
Part of T438