getaddresstxids RPC should have a single struct argument, not multiple arguments

[teor2345]

Motivation

When I run this command against zcashd it works:

zcash-cli getaddresstxids '{"addresses": ["t3LmX1cxWPPPqL4TZHx42HU3U5ghbFjRiif"], "start": 1000, "end": 2000}'

But when I run it against Zebra, it fails:

zcash-cli -rpcport="$ZEBRAD_RPC_PORT" '{"addresses": ["t3LmX1cxWPPPqL4TZHx42HU3U5ghbFjRiif"], "start": 1000, "end": 2000}'

With this error:

error code: -32602
error message:
Invalid params: invalid length 1, expected a tuple of size 3.

This check needs the fix in PR #4215.

Designs

It looks like Zebra should take a single struct argument with named fields, rather than multiple named arguments.

This appears to be the only lightwalletd request with multiple named fields:
https://github.com/zcash/lightwalletd/blob/bdaac63f3ee0dbef62bde04f6817a9f90d483b00/common/common.go#L97