Build: Move wallet RPCs to their own libbitcoin_walletrpcs module #18469

Attempt to fix #18465. This also trims the RPC code out of the bitcoin-wallet build.

The build currently fails for bench_bitcoin for reasons I can't figure out.

Also, I'm not really sure what is needed for MSVC.

Chasing Concept ACKs for now (or ideas for alternative directions, please post to #18465 )

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #18471 (qa: Test shared validation interface by promag)
• #18354 (Protect wallet by using shared pointers by bvbfan)
• #18338 (Fix wallet unload race condition by promag)
• #17999 (refactor: Add ChainClient setMockTime, getWallets methods by ryanofsky)
• #16923 (wallet: Handle duplicate fileid exception by promag)
• #16549 ([WIP] UI external signer support (e.g. hardware wallet) by Sjors)
• #16546 ([WIP] External signer support - Wallet Box edition by Sjors)
• #16367 (Multiprocess build support by ryanofsky)
• #10102 ([experimental] Multiprocess bitcoin by ryanofsky)

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.

I will be honest and say I don't really understand how this PR is trying to organize the libraries and API, but I did post an alternate fix #18465 (comment) that I think addresses the problem simply and directly

@ryanofsky The point here is to only link wallet RPC stuff when there is a RPC server (and therefore urlDecode)