rpc: Add option to hide RPCArg

Summary:
Also, update switch statments to our style guide

This is a backport of core#19386 [4/5]
https://github.com/bitcoin/bitcoin/pull/19386/commits/aaaaad562790cd4dce1568ae193f5393aacacedf

Depends on D10008

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D10009