Move txoutproof RPCs to txoutproof.cpp #24582

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.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #24539 (Add a "tx output spender" index by sstone)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

Concept and code-review ACK fa2d176016683eac82dabfbfc276b8a7b07b7499

ACK fa2d176016683eac82dabfbfc276b8a7b07b7499