wallet: MarkDirty after AddWalletDescriptor

After adding a wallet descriptor (typically by import), mark all balance
caches dirty. This allows transactions that the wallet already knows
about that have outputs that are now ISMINE_SPENDABLE after the import
to actually be shown in balance calculations. Legacy wallet imports
would do this, but importdescriptors did not.

src/wallet/wallet.cpp

@@ -3735,6 +3735,9 @@ util::Result<std::reference_wrapper<DescriptorScriptPubKeyMan>> CWallet::AddWall
     // Save the descriptor to DB
     spk_man->WriteDescriptor();
 
+    // Break balance caches so that outputs that are now IsMine in already known txs will be included in the balance
+    MarkDirty();
+
     return std::reference_wrapper(*spk_man);
 }