Rename Balance::claimable_amount_satoshis to have a unique name

In Java/TypeScript, we map enums as a base class and each variant
as a class which extends the base. In Java/TypeScript, functions
and fields share the same namespace, which means we cannot have
functions on an enum which have the same name as any fields in any
enum variants.

`Balance`'s `claimable_amount_satoshis` method aliases with fields
in each variant, and thus ultimately doesn't compile in TypeScript.

Because `Balance::claimable_amount_satoshis` has the same name as
the fields, it's also a bit confusing, as it doesn't return the
field for each variant, but sometimes returns zero if we're not
sure we can claim the balance.

Instead, we rename the method
`definitely_claimable_amount_satoshis`.

Author: TheBlueMatt

lightning/src/chain/channelmonitor.rs

@@ -654,7 +654,7 @@ impl Balance {
 	/// [`Balance::MaybePreimageClaimableHTLC`].
 	///
 	/// On-chain fees required to claim the balance are not included in this amount.
-	pub fn claimable_amount_satoshis(&self) -> u64 {
+	pub fn definitely_claimable_amount_satoshis(&self) -> u64 {
 		match self {
 			Balance::ClaimableOnChannelClose {
 				claimable_amount_satoshis,