Merge #12559: Avoid locking cs_main in some wallet RPC

Summary:
00f58f8c48db05dce9dceed73a0028482e037f0f rpc: Avoid locking cs_main in some wallet RPC (João Barbosa)

Pull request description:

Avoid locking `cs_main` in the folllowing wallet RPC:
 - `decoderawtransaction`
 - `getnewaddress`
 - `getrawchangeaddress`
 - `setlabel`

Tree-SHA512: 54089766b2a969a17479af6c60e8ce151fac1f8cec268d43c61e679d5d17e76d17e414240c9ca2bfd280165f3a04e24a51310eb283591cd601a7eebc8b2423ea

Backport of Core PR12559
https://github.com/bitcoin/bitcoin/pull/12559/

Test Plan:

cmake -GNinja -DCMAKE_BUILD_TYPE=Debug ..
ninja check-all

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4930