Make ChainMonitor::get_claimable_balances take a slice of refs

For the same reason as `get_route`, a slice of objects isn't
practical to map to bindings - the objects in the bindings space
are structs with a pointer and some additional metadata. Thus, to
create a slice of them, we'd need to take ownership of the objects
behind the pointer, place them into a slace, and then restore them
to the pointer.

This would be a lot of memory copying and marshalling, not to
mention wouldn't be thread-safe, which the same function otherwise
would be if we used a slice of references instead of a slice of
objects.

Author: TheBlueMatt

lightning/src/chain/chainmonitor.rs

@@ -150,7 +150,7 @@ where C::Target: chain::Filter,
 	///
 	/// See [`ChannelMonitor::get_claimable_balances`] for more details on the exact criteria for
 	/// inclusion in the return value.
-	pub fn get_claimable_balances(&self, ignored_channels: &[ChannelDetails]) -> Vec<Balance> {
+	pub fn get_claimable_balances(&self, ignored_channels: &[&ChannelDetails]) -> Vec<Balance> {
 		let mut ret = Vec::new();
 		let monitors = self.monitors.read().unwrap();
 		for (_, monitor) in monitors.iter().filter(|(funding_outpoint, _)| {