The txoutproof RPCs don't really fit into rawtransaction.cpp, as they deal with txids, not with raw transactions. As they are placed in the blockchain RPC category, they could be moved there. However, blockchain.cpp already takes about 20 seconds to compile (and rawtransaction.cpp even longer), so move them to a separate file.
Can be reviewed with --color-moved=dimmed-zebra --color-moved-ws=ignore-all-space
This is a backport of core#24582