Pass Nonce directly to InvoiceRequestBuilder

Pass Nonce directly to InvoiceRequestBuilder

When using InvoiceRequestBuilder::deriving_payer_id, the nonce generated
needs to be the same one included in any reply path. This is because the
nonce is used along with the invoice request TLVs to derive a payer id.
While this data is also included in the payer_metadata, including it in
the blinded path would allow reducing the amount of data needed there to
just enough to provide entropy (i.e., 16 bytes). This is more important
for Refund because it can be transmitted via a QR code. But using the
same payer_metadata structure for both InvoiceRequest and Refund would
be beneficial to avoid more code.