Post-0.21: Separate wallet and node

In https://github.com/bitcoin/bitcoin/pull/16367 the various Bitcoin Core were largely separated. In the 0.21 rebase of this PR I added `libbitcoin_common_a_SOURCES` and `libbitcoin_server_a_SOURCES` to `libbitcoin_wallet_a_SOURCES` which partially undid this separation.

The reason for this was that the blocksigning RPCs, while being part of the wallet, need access to the node. Similarly the pegin RPCs also look at the current chain state and even accesses the Bitcoin RPC.

Properly separating these things may be nontrivial. Blocksigning we should likely just move to a separate utility rather than being part of the wallet. Pegin claim management will take more thought.

PR #16367 と 0.21 rebase から始め、続いて libbitcoin_wallet_a_SOURCES を libbitcoin_common_a_SOURCES および libbitcoin_server_a_SOURCES と併せて調べます。blocksigning RPC と pegin RPC を追跡し、それらの node および chain-state への依存関係を理解します。必要な RPC の動作を失わずに wallet の分離が復元されれば完了です。

索引モデルが issue の本文から書いたものです。