refactor: Pass chainstate parameters to MaybeCompleteSnapshotValidation

Remove hardcoded references to m_ibd_chainstate and m_snapshot_chainstate so
MaybeCompleteSnapshotValidation function can be simpler and focus on validating
the snapshot without dealing with internal ChainstateManager states.

This is a step towards being able to validate the snapshot outside of
ActivateBestChain loop so cs_main is not locked for minutes when the snapshot
block is connected.

src/node/utxo_snapshot.cpp

@@ -81,7 +81,7 @@ std::optional<uint256> ReadSnapshotBaseBlockhash(fs::path chaindir)
     return base_blockhash;
 }
 
-std::optional<fs::path> FindSnapshotChainstateDir(const fs::path& data_dir)
+std::optional<fs::path> FindAssumeutxoChainstateDir(const fs::path& data_dir)
 {
     fs::path possible_dir =
         data_dir / fs::u8path(strprintf("chainstate%s", SNAPSHOT_CHAINSTATE_SUFFIX));