Continuation of wallet boxes project.
Actually makes ScriptPubKeyMan an interface which LegacyScriptPubkeyMan. Moves around functions and things from CWallet into LegacyScriptPubKeyMan so that they are actually separate things without circular dependencies.
Introducing the ScriptPubKeyMan (short for ScriptPubKeyManager) for managing scriptPubKeys and their associated scripts and keys. This functionality is moved over from CWallet. Instead, CWallet will have a pointer to a ScriptPubKeyMan for every possible address type, internal and external. It will fetch the correct ScriptPubKeyMan as necessary. When fetching new addresses, it chooses the ScriptPubKeyMan based on address type and whether it is change. For signing, it takes the script and asks each ScriptPubKeyMan for whether that ScriptPubKeyMan considers that script IsMine, whether it has that script, or whether it is able to produce a signature for it. If so, the ScriptPubKeyMan will provide a SigningProvider to the caller which will use that in order to sign.
There is currently one ScriptPubKeyMan - the LegacyScriptPubKeyMan. Each CWallet will have only one LegacyScriptPubKeyMan with the pointers for all of the address types and change pointing to this LegacyScriptPubKeyMan. It is created when the wallet is loaded and all keys and metadata are loaded into it instead of CWallet. The LegacyScriptPubKeyMan is primarily made up of all of the key and script management that used to be in CWallet. For convenience, CWallet has a GetLegacyScriptPubKeyMan which will return the LegacyScriptPubKeyMan or a nullptr if it does not have one (not yet implemented, but callers will check for the nullptr). For purposes of signing, LegacyScriptPubKeyMan’s GetSigningProvider will return itself rather than a separate SigningProvider. This will be different for future ScriptPubKeyMans.
The LegacyScriptPubKeyMan will also handle the importing and exporting of keys and scripts instead of CWallet. As such, a number of RPCs have been limited to work only if a LegacyScriptPubKeyMan can be retrieved from the wallet. These RPCs are sethdseed, addmultisigaddress, importaddress, importprivkey, importpubkey, importmulti, dumpprivkey, and dumpwallet. Other RPCs which relied on the wallet for scripts and keys have been modified in order to take the SigningProvider retrieved from the ScriptPubKeyMan for a given script.
Overall, these changes should not effect how everything actually works and the user should experience no difference between having this change and not having it. As such, no functional tests were changed, and the only unit tests changed were those that were directly accessing CWallet functions that have been removed.
This PR is the last step in the Wallet Structure Changes.
