Merge bitcoin/bitcoin#28724: wallet: Cleanup accidental encryption keys in watchonly wallets

69e95c2b4f tests: Test cleanup of mkeys from wallets without privkeys (Andrew Chow)
2b9279b50a wallet: Remove unused encryption keys from watchonly wallets (Andrew Chow)
813a16a463 wallet: Add HasCryptedKeys (Andrew Chow)

Pull request description:

  An earlier version allowed users to create watchonly wallets (wallets without private keys) that were "encrypted". Such wallets would have a stored encryption keys, but nothing would actually be encrypted with them. This can cause unexpected behavior such as https://github.com/bitcoin-core/gui/issues/772.

  We can detect such wallets as they will have the disable private keys flag set, no encrypted keys, and encryption keys. For such wallets, we can remove those encryption keys thereby avoiding any issues that may result from this unexpected situation.

ACKs for top commit:
  sipa:
    utACK 69e95c2b4f.
  laanwj:
    Code review re-ACK 69e95c2b4f
  furszy:
    Code review ACK 69e95c2b4f

Tree-SHA512: 901932cd709c57e66c598f011f0105a243b5a8b539db2ef3fcf370dca4cf35ae09bc1110e8fca8353be470f159468855a4dd96b99bc9c1112adc86ccc50e1b9d

src/wallet/scriptpubkeyman.cpp

@@ -525,6 +525,12 @@ bool LegacyScriptPubKeyMan::HavePrivateKeys() const
     return !mapKeys.empty() || !mapCryptedKeys.empty();
 }
 
+bool LegacyScriptPubKeyMan::HaveCryptedKeys() const
+{
+    LOCK(cs_KeyStore);
+    return !mapCryptedKeys.empty();
+}
+
 void LegacyScriptPubKeyMan::RewriteDB()
 {
     LOCK(cs_KeyStore);
@@ -2411,6 +2417,12 @@ bool DescriptorScriptPubKeyMan::HavePrivateKeys() const
     return m_map_keys.size() > 0 || m_map_crypted_keys.size() > 0;
 }
 
+bool DescriptorScriptPubKeyMan::HaveCryptedKeys() const
+{
+    LOCK(cs_desc_man);
+    return !m_map_crypted_keys.empty();
+}
+
 std::optional<int64_t> DescriptorScriptPubKeyMan::GetOldestKeyPoolTime() const
 {
     // This is only used for getwalletinfo output and isn't relevant to descriptor wallets.