Implement IsMine for DescriptorScriptPubKeyMan

Adds a set of scriptPubKeys that DescriptorScriptPubKeyMan tracks.
If the given script is in that set, it is considered ISMINE_SPENDABLE

src/wallet/scriptpubkeyman.cpp

@@ -1507,6 +1507,10 @@ bool DescriptorScriptPubKeyMan::GetNewDestination(const OutputType type, CTxDest
 
 isminetype DescriptorScriptPubKeyMan::IsMine(const CScript& script) const
 {
+    LOCK(cs_desc_man);
+    if (m_map_script_pub_keys.count(script) > 0) {
+        return ISMINE_SPENDABLE;
+    }
     return ISMINE_NO;
 }
 
@@ -1580,7 +1584,7 @@ std::unique_ptr<SigningProvider> DescriptorScriptPubKeyMan::GetSolvingProvider(c
 
 bool DescriptorScriptPubKeyMan::CanProvide(const CScript& script, SignatureData& sigdata)
 {
-    return false;
+    return IsMine(script);
 }
 
 bool DescriptorScriptPubKeyMan::SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, std::string>& input_errors) const