This commit squashes the below operations for a net result where
we have an expanded capability of assessing pending updates. This
is made possible by packing the components into Duals in the prior
commits. We squash the operations to simplify review.
htlcswitch+lnwallet: rename PendingLocalUpdateCount
lnwallet: complete pending update queries API for LightningChannel
lnwallet+htlcswitch: consolidate NumPendingUpdates using ChannelParty
This commit makes the observation that we can cleanly define the
NumPendingUpdates function using a single expression by taking
advantage of the relevant fields being properly packed into Duals.
1422729f80