BIP-0350: use bech32m for witness version 1+ addresses

We have supported sending to any witness version since Electrum 3.0, using
addresses as specified in BIP-0173 (bech32 encoding).
BIP-0350 makes a breaking change in address encoding, and recommends using
(and using only) a new encoding (bech32m) for sending to witness version 1
and later. The address encoding for currently in use witness v0 addresses
remains the same, as in BIP-0173; following the BIP-0350 spec.

closes https://github.com/spesmilo/electrum/issues/6949

related:
cd3885c0fb/bip-0350.mediawiki
https://github.com/bitcoin/bitcoin/pull/20861

electrum/tests/test_bolt11.py

@@ -6,6 +6,7 @@ import unittest
 
 from electrum.lnaddr import shorten_amount, unshorten_amount, LnAddr, lnencode, lndecode, u5_to_bitarray, bitarray_to_u5
 from electrum.segwit_addr import bech32_encode, bech32_decode
+from electrum import segwit_addr
 from electrum.lnutil import UnknownEvenFeatureBits, derive_payment_secret_from_payment_preimage, LnFeatures
 
 from . import ElectrumTestCase
@@ -114,20 +115,21 @@ class TestBolt11(ElectrumTestCase):
     def test_n_decoding(self):
         # We flip the signature recovery bit, which would normally give a different
         # pubkey.
-        hrp, data = bech32_decode(lnencode(LnAddr(paymenthash=RHASH, amount=24, tags=[('d', '')]), PRIVKEY), True)
+        _, hrp, data = bech32_decode(
+            lnencode(LnAddr(paymenthash=RHASH, amount=24, tags=[('d', '')]), PRIVKEY),
+            ignore_long_length=True)
         databits = u5_to_bitarray(data)
         databits.invert(-1)
-        lnaddr = lndecode(bech32_encode(hrp, bitarray_to_u5(databits)), verbose=True)
+        lnaddr = lndecode(bech32_encode(segwit_addr.Encoding.BECH32, hrp, bitarray_to_u5(databits)), verbose=True)
         assert lnaddr.pubkey.serialize() != PUBKEY
 
         # But not if we supply expliciy `n` specifier!
-        hrp, data = bech32_decode(lnencode(LnAddr(paymenthash=RHASH, amount=24,
-                                                  tags=[('d', ''),
-                                                        ('n', PUBKEY)]),
-                                           PRIVKEY), True)
+        _, hrp, data = bech32_decode(
+            lnencode(LnAddr(paymenthash=RHASH, amount=24, tags=[('d', ''), ('n', PUBKEY)]), PRIVKEY),
+            ignore_long_length=True)
         databits = u5_to_bitarray(data)
         databits.invert(-1)
-        lnaddr = lndecode(bech32_encode(hrp, bitarray_to_u5(databits)), verbose=True)
+        lnaddr = lndecode(bech32_encode(segwit_addr.Encoding.BECH32, hrp, bitarray_to_u5(databits)), verbose=True)
         assert lnaddr.pubkey.serialize() == PUBKEY
 
     def test_min_final_cltv_expiry_decoding(self):