Support fetching 'verifiable' transactions

[kayabaNerve]

Right now, transactions can be fetched as either full transactions or as pruned transactions, where they have no signatures and solely the hash of their signatures. For version 2 transactions, this is sufficient to calculate the transaction's hash. For version 1, it is not. Anyone who wishes to verify the version 1 transaction is the requested transaction must make a follow-up request for the full version 1 transaction.

Ideally, I can flag I want verifiable transactions, defined as:

• Full V1 transactions
• Pruned V2 transactions, with the hashes of their prunable sections

This can potentially be done simply. For the following block,

monero/src/rpc/core_rpc_server.cpp

Lines 1137 to 1142 in 8e9ab96

	if (req.split || req.prune || pruned)
	{
	// use split form with pruned and prunable (filled only when prune=false and the daemon has it), leaving as_hex as empty
	e.pruned_as_hex = string_tools::buff_to_hex_nodelimer(std::get<1>(tx));
	if (!req.prune)
	e.prunable_as_hex = string_tools::buff_to_hex_nodelimer(std::get<3>(tx));

(!req.prune || (v1_transaction && req.verifiable))

may be sufficient as an alternative condition on the if check. This would resolve it for /get_transactions, but ideally the same change is also made for /get_blocks.bin and any other methods returning potentially-pruned transactions.

[kayabaNerve]

include_v1_ring_signatures may be a more straightforward name.