Allow RPC methods which take an options parameter (importmulti, listunspent, fundrawtransaction, bumpfee, send, sendall, walletcreatefundedpsbt, simulaterawtransaction), to accept the options as named parameters, without the need for nested JSON objects.

This makes it possible to make calls like:

src/bitcoin-cli -named bumpfee txid fee_rate=10

instead of

src/bitcoin-cli -named bumpfee txid options='{"fee_rate": 10}'

RPC help is also updated to show options as top level named arguments instead of as nested objects.
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ninja all check-all