core/types: ensure receipts EncodeIndex writes + support blobtx-receipts

[holiman]

This PR fixes an issue which can happen on blob-tx-testnets, where we try to encode the receipt of a blob-transaction, but ends up writing nothing: which is "deletion" as far as the stacktrie is concerned, causing panic.

This PR does two things:

• Always write type first, thereby making sure that even unsupported things cause a write of at least one byte,
• Add support for blob receipts.

As for the second bullet, a different way of doing it would be to do what the transactions already does

	if tx.Type() == LegacyTxType {
		rlp.Encode(w, tx.inner)
	} else {
		tx.encodeTyped(w)
	}
}

func (tx *Transaction) encodeTyped(w *bytes.Buffer) error {
	w.WriteByte(tx.Type())
	return rlp.Encode(w, tx.inner)
}

Simply write type ... rlp(data) for typed data. That way we wouldn't have to bother with "adding support for type x", it would just work.

I don't know which is best, I currently left it as is.