This commit adds encoding and decoding for blinded route data blobs.
TLV fields such as path_id (which are only used for the final hop)
are omitted to minimize the change size.
This commit adds the encrypted_data, blinding_point and total_amt_msat
tlvs to the known set of even tlvs for the onion payload. These TLVs
are added in two places (the onion payload and hop struct) because
lnd uses the same set of TLV types for both structs (and they
inherently represent the same thing).
Note: in some places, unit tests intentionally mimic the style
of older tests, so as to be more consistently readable.
This commit adds handling code for the key send custom record. If this
record is present and its hash matches the payment hash, invoice
registry will insert a new invoice into the database "just in time". The
subsequent settle flow is unchanged. The newly inserted invoice is
picked up and settled. Notifications will be broadcast as usual.
