Merge #20494: refactor: Move node and wallet code out of src/interfaces

629a929 Move WalletImpl from interfaces/wallet.cpp to wallet/interfaces.cpp (Russell Yanofsky)
2a26771 Move ChainImpl from interfaces/chain.cpp to node/interfaces.cpp (Russell Yanofsky)
12bd0fc Move NodeImpl from interfaces/node.cpp to node/interfaces.cpp (Russell Yanofsky)

Pull request description:

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).

  ---

  Move `NodeImpl` from `interfaces/node.cpp` to `node/interfaces.cpp`
  Move `ChainImpl` from `interfaces/chain.cpp` to `node/interfaces.cpp`
  Move `WalletImpl` from `interfaces/wallet.cpp` to `wallet/interfaces.cpp`

  No changes to any classes (can review with `git diff --color-moved=dimmed_zebra`)

  Motivation for this change is to move node and wallet code to respective directories where it might fit in better than `src/interfaces/`, but also to remove all unnecessary code from `src/interfaces/` to unblock #19160 review, which has been hung up partially because of code organization. Building on top of this PR, #19160 should now be able to organize interface implementations more understandably in `src/node/` `src/wallet/` `src/ipc/` and `src/init/` directories instead of having so much functionality all in `src/interfaces/`

ACKs for top commit:
  promag:
    Code review ACK 629a929.
  MarcoFalke:
    review ACK 629a929 🔺

Tree-SHA512: 87c2b8fd51519bbd4e5ad3539a79debcf88c3bf021eb28c63f3f555186538b62a0c4cc1a3f07cfb4ff13aea8b0b2fdde505d81f22a5e5fd12a6e375b55a92ab8

Author: MarcoFalke

src/Makefile.am

@@ -298,14 +298,13 @@ libbitcoin_server_a_SOURCES = \
   index/blockfilterindex.cpp \
   index/txindex.cpp \
   init.cpp \
-  interfaces/chain.cpp \
-  interfaces/node.cpp \
   miner.cpp \
   net.cpp \
   net_processing.cpp \
   node/coin.cpp \
   node/coinstats.cpp \
   node/context.cpp \
+  node/interfaces.cpp \
   node/psbt.cpp \
   node/transaction.cpp \
   node/ui_interface.cpp \
@@ -358,13 +357,13 @@ endif
 libbitcoin_wallet_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) $(SQLITE_CFLAGS)
 libbitcoin_wallet_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 libbitcoin_wallet_a_SOURCES = \
-  interfaces/wallet.cpp \
   wallet/coincontrol.cpp \
   wallet/context.cpp \
   wallet/crypter.cpp \
   wallet/db.cpp \
   wallet/feebumper.cpp \
   wallet/fees.cpp \
+  wallet/interfaces.cpp \
   wallet/load.cpp \
   wallet/rpcdump.cpp \
   wallet/rpcwallet.cpp \