[rpc] Fix issue: "Negative version of transaction using json-rpc" #12430

In case that it is a valid issue, this PR fixes #11561 ("Negative version of transaction using json-rpc").

The verbose output of the getrawtransaction RPC gives a response with a negative transaction version number if the MSB of the transaction version number is set.

This behavior can easily be reproduced by requesting the verbose transaction data of Mainnet transaction c659729a7fea5071361c2c1a68551ca2bf77679b27086cc415adeeb03852e369, via the getrawtransaction RPC, which gives a response with a negative transaction version number:

{
  ...
  "version": -1703168784,
  ...
}

To fix the issue, commit 42df694 casts the transaction version number to an uint64_t and masks off its most significant 32 bits to pass a positive transaction version number to UniValue::pushKV(const std::string&, uint64_t):bool.

In the case of the example above it gives a response with a positive transaction version number:

{
  ...
  "version": 2591798512,
  ...
}

This transaction version number is equal to the transaction version number created by block explorers that show a positive transaction version number. See for example:

Transaction c659729a7fea5071361c2c1a68551ca2bf77679b27086cc415adeeb03852e369 on Blockcypher.com

Negative transaction versions are negative, the distinction is not just cosmetic. There is protocol behavior e.g. interpretation of sequence numbers for CSV that depends on the version being over a threshold.

Thanks @gmaxwell!

I should not have followed up to #11561 by submitting a PR that breaks the RPC output. The eagerness to contribute clouded my better judgement. Apologies for that.