refactor: move address_to_scriptpubkey to address.py

The COINBASE_MATURITY constant in blocktools.py is imported in wallet.py.
However, importing address_to_scriptpubkey to blocktools.py will
generate a circular import error. Since the method is related to
addresses, it is best to move it to address.py, which will also
fix the circular import error.

Update imports of address_to_scriptpubkey accordingly.

test/functional/rpc_scantxoutset.py

@@ -3,12 +3,12 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test the scantxoutset rpc call."""
+from test_framework.address import address_to_scriptpubkey
 from test_framework.messages import COIN
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal, assert_raises_rpc_error
 from test_framework.wallet import (
     MiniWallet,
-    address_to_scriptpubkey,
     getnewdestination,
 )