d8b12a75db rpc: Allow named and positional arguments to be used together (Ryan Ofsky)
Pull request description:
It's nice to be able to use named options and positional arguments together.
Most shell tools accept both, and python functions combine options and arguments allowing them to be passed with even more flexibility. This change adds support for python's approach so as a motivating example:
```sh
bitcoin-cli -named createwallet wallet_name=mywallet load_on_startup=1
```
Can be shortened to:
```sh
bitcoin-cli -named createwallet mywallet load_on_startup=1
```
JSON-RPC standard doesn't have a convention for passing named and positional parameters together, so this implementation makes one up and interprets any unused `"args"` named parameter as a positional parameter array.
This change is backwards compatible. It doesn't change the interpretation of any previously valid calls, just treats some previously invalid calls as valid.
Another use case even if you only occasionally use named arguments is that you can define an alias:
```
alias bcli='bitcoin-cli -named'
```
And now use both named named and unnamed arguments from the same alias without having to manually add `-named` option for named arguments or see annoying error "No '=' in named argument... this needs to be present for every argument (even if it is empty)`" for unnamed arguments
ACKs for top commit:
achow101:
ACK d8b12a75db
stickies-v:
re-ACK d8b12a75d
aureleoules:
re-ACK d8b12a75db
Tree-SHA512: 0cff8b50f584bcbbd376624adccf40536566ed8d1bcd6c88ad565dbc208f19d5e7a48c994efd6329d42b560149340d330397278f08a2912af5f3418d8c8837a9
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