prepare a channel to have anchors

* add anchor ln features
* peer.use_anchors is added
* channel.has_anchors is added

electrum/lnchannel.py

@@ -496,6 +496,9 @@ class AbstractChannel(Logger, ABC):
         """
         pass
 
+    def has_anchors(self) -> bool:
+        pass
+
 
 class ChannelBackup(AbstractChannel):
     """
@@ -883,6 +886,10 @@ class Channel(AbstractChannel):
             assert self.lnworker.wallet.is_mine(addr)
         return addr
 
+    def has_anchors(self) -> bool:
+        channel_type = ChannelType(self.storage.get('channel_type'))
+        return bool(channel_type & ChannelType.OPTION_ANCHOR_OUTPUTS)
+
     def get_wallet_addresses_channel_might_want_reserved(self) -> Sequence[str]:
         assert self.is_static_remotekey_enabled()
         our_payment_pubkey = self.config[LOCAL].payment_basepoint.pubkey